This is Luanti! It's a free, open source voxel game engine inspired by Minecraft. It is built from the ground up for mod support. It's very extensible and, unlike Minecraft, doesn't require any fiddling with custom launchers, mod loaders, or mod packs…even in multiplayer!
Download the game here, or use your package manager to install it. No mod download or account setup required. Please be mindful of potentially outdated versions provided by your package manager.
Joining has been secured from random people outside of ~town by requiring a secret default password. This password is posted on the BBJ thread on tilde.town and in the topic for the #asuna IRC channel. If you are unable to locate this for any reason, ask in the IRC channel or otherwise ask existing players.
How to join:
For subsequent logins, use the password you chose instead of the default one.