I went with plugin-first approach focusing on plugin APIs, everything builtin plugins provide (and more) can be also implemented by any plugin. At the moment API surface is minimal but usable, I want to work on creating plugin documentation before extending it further.
Plugins are distributed as part of Git repository, meaning no central server is required.
For JS runtime Gauntlet is using using Deno, which, among other things, gives nice security model allowing to be explicit about things plugins can do on your system.
Gauntlet is also designed with cross-platform in mind from the start. Currently supporting Linux with macOS and Windows support coming in near future.
Please join Discord server if you want to follow for updates or interested in creating a plugin. You can find the link in the beginning of the README. It is currently pretty empty in here but hopefully not for long.