[avian]

Probably not on Steam, but maybe still somewhere on the net. There used to be an open source game for unix-like systems simply called "atc" that gave you a text-mode view of a radar screen. You gave directions to pilots using the keyboard through some abbreviated text instructions. I know because it was pretty popular among some friends of mine back in the day.

I made a patch that made it a multiplayer networked game where each player controlled the space of one airport. When I was doing that I remember being surprised how the entire game was written as a parser in lex (or maybe yacc? not sure anymore) not straight C.