Spearmint is a fork of the ioquake3 engine that adds in Ogg Vorbis and Ogg Opus support by default, out-of-the-box FreeType font handling, split-screen gaming support, an improved virtual machine, and other engine enhancements. Watermint in turn is a version of Spearmint that seeks to be used with realistic first person shooters.
The Spearmint engine code is still progressing with the latest commit being one day ago. When going to the original GitHub project page for Watermint, it is no longer there. However, it turns out that it's been turned into its own Watermint Game.
As of last week on GitHub is now the Watermint-Game. The Watermint Game now consists of Watermint bots, the Watermint engine code itself that is still striving to be a realistic version of Spearmint, and the Watermint data files. The Watermint data files are for the Watermint game itself or Watermint-based games.
The game data files are CC-BY-SA 3.0 but before getting too excited, the data files are incomplete and seem to be 2D graphics and some simple artwork from Turtle Arena, one of many open-source games with really disappointing art assets.
Besides the previously talked about Spearmint/Watermint engine features, other advertised capabilities include reloading, upscaled health and damage, custom classes, locational damage, improved weapon modification, more local client visual settings, Apple iOS support, extended API, and capsule collision support.
Hopefully this game engine will become something useful and used rather than yet-another-ioquake3 fork powering nothing or just projects with rather poor artwork and no original gameplay, but we'll have to wait and see.