2.2.1 is the latest stable and official release.
The notes on the project page refer to 2.3, which is in development.
2.3 has a lot of different features, and is very different, but isn't finished yet and has many bugs.
If you want to try 2.3, look for a link for a binary to download from this forum - Odie and myself link to Windows installers, and someone whose name I forgot started Mac installers. If you're on Linux, it is very easy to download and compile the game with the wiki instructions, and you don't need to be a programmer (for Linux setup).