Terminal Phase is a side-scrolling shoot-em-up in the Gradius and R-Type tradition, but in text mode. In the terminal! It’s free software created by Christopher Lemmer Webber [Patreon].
The game is completely playable and is a fun game (well, at least a number of playtesters told me they thought it was fun). It includes two levels (one of which is more balanced than the other), and more content is on its way (1.0 isn’t the end!). You can see it being played above in cool-retro-term but it works in all sorts of terminals, including gnome-terminal and etc. I also released a video recently (archive.org mirror) of me doing a live playtest of the game and also showing off how to make new levels and program new enemies (which serves as kind of an introduction, but probably not the best one, to Spritely Goblins).
One of the first games I had as a youngster was Harrier Attack, which was essentially the same idea of a textmode side-scrolling shooter, albeit with redefined characters to try and get it looking “better”. It was not great.