In 2015, we did 3.7 which had a lot of novelties, visual polish and a new interface.
In 2016, we intensively worked on 3.8 which was a massive overhaul/polish update, we added many ease-of-use features, new options, optimizations, sounds, mechanics, many items, a re-balance, a few new KHO, revamped troop trees, overhauled scenes, bugfixes, a complete visual overhaul...
We're working on 3.9 currently, which is less massive than 3.8, but with some interesting features and a loooooot of polish and bugfixes.
The whole 3.8 changelog is
here