Globulation 2 https://globulation2.org/wiki/Main_Page It's an RTS focused on macro instead of micro. It is cross platform and supports multiplayer! It's really simple in the sense that there are only three unit types, but the strategy is much more nuanced. One interesting dynamic I appreciate is that your unit limit is caused by the fact you have to be able to feed everyone, as opposed to some arbitrary max number the game picks for you or how many pylons you've built. (What do pylons do anyway?) The AI is challenging at harder levels and I still haven't mastered beating them regularly. I really enjoy this game