Beyond All Reason (open source with FOSS engine), Stormgate (proprietary but made by ex-SC2 devs) are separate attempts at what I would call innovating the RTS genre.
AoE2 DE by Microsoft is tried, true and super popular still but many aspects are still from the original game 20 years ago. AoE 4 seems to kind of be the attempt at improving the formula, seems okay.
The Starcraft 2 engine is amazing but now under Microsoft ownership, I was hopeful initially but it looks as though it will continue to be left to rot. If only they could give it a Halo makeover using the same engine that would be awesome.