There are some obvious choices for terminal-based software — newsreaders, text editors, even file managers, to a degree.
Text-based games should be clear winners too. Here’s nsudoku, which is about as text-based as you can get.
Basic four-key movement, one key to delete and a few more to quit or restart, and that’s the basics of the game.
I can’t tell you what happens when you win, if there are ascii fireworks or digitized dancing bears. I’m a rotten sudoku player, as it would happen.
But I do appreciate a decent game for the console when I see one. 🙂