Terminal-based scriptable text editor, continuation of one of the first interactive programs in the world (vi), so it has a lot of legacy User Experience, which seems unintuitive for modern users. For instance, it does not automatically write when you launch a program. Instead, you are set in so-called "Normal mode", which maps all the keyboard keys to text-editing macros and acts as a bridge between "Insert mode" (for typing text) and "Command mode" (for application control and . If you're on "Insert mode" and want to save your edits and quit, you need to press ESC, to switch back to the Normal mode, and type in :wq and press Enter.