Riot. Radiant was merged into riot and doesn’t exist anymore, aside from the splash logo when the game starts.
In my time here in the forum I have seem so far 5 or 6 topics about “playable enemy factions”. But they never went farther then a few screenshots of reskins, always lasting just a few weeks before the author disappearing.
The only actually playable I saw was the [Mod] (A20) The Bastioneers! More Dangerous (and Mod-Friendly) Than Ever! Help me test for A20! which was really good, it was not just a reskinned kingdom with a few extra items. But it does not work now.
And the Nihonjin: Japanese Themed Mod [On Hold] which I never was able to play because when I started here it was already offline. I do not understand why he doesn’t release it as it looks pretty good already.
Then there is also those in the workshop. Boxlings and Nordlings are really good and complete/polished. Amberstone is just Northern Alliance with bunnies body which causes a lot of errors.
Easier than most other games. There are things here that are hard and require programming skills, but there are many that are done simple changing values in a text file. We have this: Stonehearth's Modding Guide It can teach you from zero