Principia

Principia is “a physics-based sandbox building game. Build and play advanced contraptions, circuiting, minigames, robot adventures and more.” It came out in November 2013 from Bithack, the studio behind the 2011 Android hit Apparatus, and was released as open source in August 2022. Since then the community has kept developing it.

What you can build

The sandbox has “200+ different objects ranging from basic wooden building blocks to circuitry, electrical and mechanical components, small robots you can control and fight against, and a LuaScript object featuring Lua scripting that can interact with the world.” The project’s own examples: “Build a controllable car, a calculator or make your own game with circuitry or in Lua.”

Everything runs on a real physics simulation, so a machine either works or falls apart. You press play to start the simulation and pause it to keep building; the labelled screenshot below shows where the controls are.

The community site

The game is tied to the community site principia-web.se, which has “tens of thousands of creative levels made by players like you”. In the project’s words: “If something really peaks your interest, open the level in the sandbox to see how it ticks.” You can also browse levels on the website and open them in the game from there.

An account there needs a username, an email address and a password, and the privacy policy advises that the username “should not be your real name”. Uploads, comments and forum posts are public.

What goes online

By default, Principia connects to principia-web.se. The privacy policy and the code agree on what happens:

• When it finishes loading, the game checks the site for a newer version and fetches the list of featured levels. (The version check is skipped when you open the game from a level link.)
• When you are logged in, it “will regularly ping the site for notifications”.
• Every request sends a user agent with the game version and your platform, for example “Principia/37 (Android) (2024.07.12)”. The site’s access logs record your IP address, user agent and referrer and “are purged on a weekly basis”, according to the policy.
• The domain can be changed or disabled with a community_host.txt file (see the questions below). F-Droid flags the app as relying on a non-free network service because the domain is built in; in October 2026 the maintainer asked F-Droid to drop that label, since the domain can now be changed or switched off.

The app asks for just two permissions, internet access and vibration, and our scan found no trackers or ad libraries.

About this file

• This is the official APK of version 2026.09.19 from the project’s GitHub releases, signed by the maintainer, Mikael Axelsson (ROllerozxa). F-Droid builds Principia separately and signs it with its own key; the project’s download page says “the F-Droid build uses a different signing key, which means that if you want to switch distribution channels you’ll need to fully uninstall Principia before installing the new version. Please back up your user data before doing so.”
• F-Droid is one version behind: its build of 2026.09.19 failed, so it still offers 2026.08.16.
• The 30.1 MB file runs on 64-bit and 32-bit ARM and 64-bit x86, from Android 5.0.
• Code and media are under the BSD 3-Clause licence, “applying both to code and media” in the project’s words; the fonts are under the SIL Open Font License. The labelled editor screenshot is from the Principia Wiki (CC BY 4.0); the others are from the project.
• The download page has a warning for players in Brazil, Indonesia, Singapore and Thailand: “you may already be blocked from installing Principia as part of Google’s early rollout beginning in September of 2026.” Our guide to Android developer verification explains what is blocked so far and what isn’t.

Licence notice

Principia is distributed under the following licence, which asks that binary copies carry it. The APK doesn’t include it, so here it is:

Copyright (c) 2012-2022 Bithack AB

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
3. The name of the author may not be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

CPU types in this build: arm64-v8a (64-bit ARM, almost every phone since 2017); armeabi-v7a (32-bit ARM, older and budget phones); x86_64 (64-bit Intel, emulators and Chromebooks).

Recent releases on the project’s GitHub. We host and check only the newest one. Full changelog.