Luanti

Minecraft is excellent, but it must be purchased, requires a Microsoft account, splits into incompatible Java and Bedrock editions, and mod installation is not simple for a child. For "I just want my kid to have a game where they can build freely" or "I want to run a server for friends", there is another option.

Luanti — renamed from Minetest in 2024 — is an open-source voxel sandbox engine. 13,446 stars, LGPL-2.1, entirely free, no account, playable immediately after install.

One thing to understand: it is more an engine than a single game. After installing, you download "games" from the built-in content browser — some close to Minecraft's formula (MineClone2, for instance), others entirely different, covering survival, building, puzzles, space and management. The structure is confusing at first, but it means one installation offers many kinds of play.

Practical strengths:

• Good performance. Written in C++ and far smoother than the Java edition, running on old computers and modest hardware including Android phones.
• Self-hosting is simple. The server is the same program, so an old machine at home suffices for playing with family and friends without renting anything. Fully offline single-player also works.
• A large mod ecosystem: thousands of mods and games installable from inside the client, with no manual file placement and no version conflicts to manage.
• Programmable. Mods and complete games are written in Lua with thorough API documentation. For a child interested in programming this is a natural entry point — change a number and see the game change.
• Effectively unlimited world size with swappable terrain generators.

To be clear about:

• It is not Minecraft and is not compatible with it. Worlds, mods and skins do not transfer, and you cannot connect to Minecraft servers. If a child wants to play the same game as their classmates, this does not substitute.
• Visual polish trails commercial products. Default textures are plain and the animation and audio are simple, so first impressions feel rough. Texture packs and a mature game mode improve this considerably.
• You must choose content yourself. Community games vary widely in quality, from complete experiences to abandoned prototypes. Start with something finished like MineClone2 or VoxeLibre.
• Non-English material is limited. The interface is localized, but community tutorials and mod documentation are mostly in English.

Who it suits: parents wanting a free building game without buying accounts, anyone running a server for friends, modest hardware, and anyone who wants to learn Lua by modifying a game.