v0.5.0 Offline 3D editor · Windows · macOS · Linux

Model in minutes. Print the same day.

A drag-and-drop 3D editor that runs fully offline. Drop in shapes, combine with booleans, export STL, hit print. No account, no cloud waiting, no upload caps. Just you and your printer.

Download for your OS See workflow
Free for personal use No account, no email Works offline Signed binaries
v0.5.0Released May 2026
13Primitive shapes
3Sketch tools
0Tracking pixels
Eiffel Tower STL — 123k triangles, live volume metrics
Eiffel · 123k tris
A modelled hinge — solids and holes grouped + baked
Hinge · CSG group + bake
Porsche 911 STL imported and orbiting in BlockBuilder Studio
Porsche 911 · 150k tris · orbited
Code-signed binaries
Zero telemetry
Files stay on your disk
Free forever, personal use
Features

Everything you need to model
for the printer. Nothing you don't.

13 primitive shapes, full CSG (union + subtraction), STL/OBJ/STEP import-export, sketches, slicing, hollowing, arrays, ruler — all running locally on your machine.

Core feature
A blue solid cylinder overlapping a red translucent hole-box, ready to be combined via Group.

Solid + Hole booleans

Toggle a shape to hole and it carves into anything it overlaps with after Group. Solids merge, holes subtract. Fully reversible until you bake. Powered by three-bvh-csg.

Export
Toolbar export buttons — Save, Upload, Import, STL, STEP, OBJ — with the OBJ tooltip showing its description.

STL · OBJ · STEP export

Printer-ready binary STL, Wavefront OBJ, or AP203 faceted-brep STEP for CAD/CAM pipelines. Bring in any mesh as an editable shape — your imports become primitives.

Sketch tools

Extrude polygons, scribble free-hand outlines, revolve profiles into lathe-style solids.

Cut along plane

Bambu-style. Slice along X, Y, or Z into two halves with a live plane preview.

Hollow / Shell

Carve the inside of any shape at a chosen wall thickness. Print-ready shells in two clicks.

Ruler · vertex snap

Click two points. Distance + per-axis deltas. Locks to vertices so measurements are exact.

Linear + circular arrays

N copies along a line with spacing, or around an axis with a chosen total angle.

Workplane on face

Drop the active workplane on any face. New shapes spawn aligned to that face's normal.

Live volume + surface area

Estimate filament cost without leaving the app.

Volume
42.18 cm³
Surface
87.41 cm²
Triangles
2,164
Real screenshots

This is what it actually looks like.

No mockups, no hand-drawn figures. The real app, real geometry, real exported STLs.

BlockBuilder Studio editing a high-detail Porsche 911 STL import — fully orbital camera, smooth shading, viewport unchanged from a primitive.
Porsche 911 import · ~150k tris · orbited, no lag
Mercedes-Benz SLS — lime-shaded STL import standing on the workplane.
Mercedes-Benz SLS · imported STL
Rhino Beetle Wrestler selected, with the Properties panel showing size, position, opacity, colour swatches, metrics (volume, surface area, tri count), and Lock / Reset / Delete actions.
Properties panel · live volume + surface area
A high-poly Eiffel Tower STL import shown in BlockBuilder with the Properties panel reporting 123k triangles and a volume of 13.43k cm³.
Eiffel Tower · 123k tris · live metrics
Sloth Yoga character STL standing on a base, lime-shaded, viewed from the front.
Sloth Yoga · imported character STL
A modelled hinge with 16 evenly spaced cylindrical holes, made by combining a box with hole cylinders via Group + Bake.
Hinge · solids + holes grouped + baked
Angry Pikachu STL import, coral-shaded, full-body.
Angry Pikachu · imported character STL
Workflow

From idea to printable STL
in four steps.

Five minutes from first launch to a printed bracket. No tutorial required.

01

Drop in a shape

Drag any of the 13 primitives from the left panel. Tweak size + segments in Properties.

02

Toggle a Hole

Mark a shape as Hole and it carves into overlapping solids on Group.

03

Group to combine

Select shapes, hit Ctrl+G. Live CSG. Reversible until you Bake.

04

Export · slice · print

Click STL. Open in Bambu Studio / Cura / PrusaSlicer. Done.

What you get

Six promises. No fine print.

Same commitments for the free version and the licensed one. Same software, same code, same respect.

Fully offline

The app never makes a network request once installed. Plane, air-gapped workstation, café Wi-Fi outage — same behaviour.

No accounts, ever

No sign-up. No email confirmation. No "verify your identity". Install and use. Commercial licences are verified offline against the local file.

No upload limits

Imports happen locally. Bring in a 500 MB STL with 5M triangles — your RAM is the only limit. BVH-accelerated picking handles it.

Your files stay yours

Saves are plain JSON on your disk. STL exports land in Downloads/. Nothing leaves your machine unless you share it.

No tracking

Zero telemetry. Zero analytics. Zero cookies. The app doesn't know you exist after install. This website doesn't either.

No subscription

Personal use is free forever. Commercial licence is €12 once, lifetime — every future update included until v1.0+.

Use cases

Built for the work,
not the workflow.

What people actually make with BlockBuilder.

3D printing

Custom replacement parts

Bracket broke? Cabinet handle missing? Measure with a calliper, model in 5 minutes, print in 30.

Prototyping

Idea to mock in an afternoon

Faster than Fusion for blocky designs. Move to parametric CAD once the proportions feel right.

Education

Classroom 3D without logins

No student accounts to set up, no schoolwide trust forms. Each PC runs its own instance.

Makers

Jigs, fixtures, organisers

Custom boxes, tool holders, drawer dividers, GoPro mounts. The boring practical stuff 3D printing is best at.

Remixers

Edit imported STLs

Pull a model off Printables, scale it, slice a section, drill a hole, re-export. No 25 MB upload cap.

Tabletop

Bases · terrain · props

Hex bases, ruined walls, simple miniatures. Star + polygon + extrude get you 80% of the way.

Pricing

Two ways to use it.
Both are fair.

Free for personal projects. €12 once for commercial use — covers the next ten years of updates.

Personal Hobby · learning · home prints
€ 0 / forever

No account, no email, no time limit. The full app.

  • Every feature — no lockouts, no nag screens you can't dismiss
  • Unlimited STL · OBJ · STEP exports
  • Free updates forever
  • Email support, best effort
Download free
Commercial
€ 12 once · lifetime

For selling prints, freelance, classroom, agency work.

  • Everything in Personal
  • Commercial licence — sell prints, freelance, agency, classroom
  • Silences the in-app reminder dialog
  • Priority email support · 48h reply
  • Lifetime updates through v1.0+
Buy commercial licence — €12
Download · v0.5.0 · ~80 MB

Pick your OS.
One click. Sixty seconds.

No email, no signup, no waitlist. The download starts immediately.

You're on a phone or tablet. BlockBuilder is desktop-only — it needs a mouse and keyboard for the 3D viewport. Open this page on your computer to download, or send yourself a link:
Windows 10 · 11
BlockBuilder-Setup.exe ~82 MB · NSIS installer · Signed
macOS 12+
BlockBuilder.dmg ~94 MB · Universal · Notarised
Linux x64
BlockBuilder.AppImage ~88 MB · Portable · No install

v0.5.0 · Released May 2026 · Signed for Windows · Notarised for macOS · See changelog →

Windows 10 / 11 · x64 · 4 GB RAM · WebGL2 (most onboard graphics from 2015+)
macOS 12 Monterey or later · Intel x64 or Apple Silicon (M1+)
Linux Ubuntu 22.04+ / Fedora 38+ / Arch / any distro with FUSE
FAQ

Questions, answered honestly.

If something here is unclear, email geral@marjers.com — replies usually within 48 hours.

Is it really free?

Yes. Free for personal use, no time limit, no feature lockout, no nag screens you can't dismiss. The €12 commercial licence is for people who use exports in for-profit work (selling prints, freelance, classroom) and silences the occasional reminder dialog. Everyone else can use it forever for €0.

Do I need an account or internet connection?

Neither. Once installed, the app never makes a network request. Your work stays on your machine. No telemetry, no analytics, no auto-uploads.

Where is my work saved?

Two places. Autosave: localStorage in the app's profile folder, restored on next launch. Project files: standard .json on disk that you save explicitly. STL/OBJ exports go wherever your downloads land (usually Downloads/).

Why does Windows show a SmartScreen warning?

Because the binary is new and SmartScreen hasn't built reputation for it yet. Click "More info" → "Run anyway" and it goes away forever for that install. Once enough people install BlockBuilder, the warning disappears for everyone. Builds are code-signed; the binary is genuinely from Marjers and contains no malware. You can verify the signature in the .exe properties.

Can I use it commercially?

Yes, with a one-time €12 commercial licence at marjers.com/blockbuilder. Covers selling prints, freelance work, paid classroom use, agency work — anything for-profit. Personal/hobby use stays free.

Is this CAD?

Not in the engineering sense. BlockBuilder is a direct modelling tool: drag primitives, scale them, combine with booleans. No parametric history, no constraints, no assemblies, no engineering drawings. It's optimised for the 80% of 3D-printing work that doesn't need those features — brackets, organisers, replacement parts, props, jigs. For mechanical engineering with version-controlled geometry, use a parametric CAD package.

Can I import existing STL or OBJ files?

Yes. Drag any .stl or .obj into the viewport (or use the Import button). Imported meshes behave like primitives: move, scale, rotate, colour, mark as Hole, group with others, run CSG against them. Big meshes (100k+ triangles) get an automatic BVH for fast picking.

Can I export to STEP?

Yes, with a caveat. BlockBuilder works internally with triangle meshes, not parametric CAD surfaces. The STEP export wraps the mesh in an AP203 faceted B-Rep file that Fusion 360, SolidWorks, FreeCAD, Onshape and most CAD/CAM tools will open as a mesh body. You won't get editable parametric features. For passing geometry to a CNC shop that requires STEP, this is a working option.

What if my STL fails the boolean operation?

Imported meshes need to be watertight (manifold) for CSG. Use the Repair button in the Properties panel: it welds duplicate vertices, drops zero-area triangles, and rebuilds normals. Resolves most failures.

Is the source code available?

Not yet. Open-sourcing is on the roadmap once the code is more polished. The Electron + Three.js stack is well-known with no proprietary dependencies, so the timeline is mostly about cleaning up.

How do I get help or report bugs?

Email geral@marjers.com with a description and, if possible, the saved .json that triggers the bug. Replies usually within 48 hours.

Touchscreens, iPads, phones?

Not supported. BlockBuilder is desktop-only (mouse + keyboard). The 3D viewport relies on right-click orbit, scroll-zoom, and precise pointer hits that don't translate to touch. A web version may come later.

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From the workshop of Marjers.

BlockBuilder Studio is built and maintained by Marjers — a small studio making honest desktop tools for makers. No VC, no growth team, no dark patterns. Software that does what it says, costs what it costs, and gets out of your way.

Visit marjers.com → Donate · buy me a coffee

Ready to model?

Free forever for personal use. No signup, no email, no credit card. Drop in shapes, hit print.

Download BlockBuilder Studio Buy commercial licence · €12

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