> "never had it in the first place" is absolutely correct.

To be clear: I didn't mean to imply this is a bad thing.

GNU's Not Unix, Pine Is Not Elm, TIP Isn't Pico all share one important characteristic — their audience is expected to know what Unix, Elm, Pico are, and saying "X is not Y" implies "X is specifically, deliberately an alternative to Y, in the same style as Y".

If you know what GNU and YACC are, you probably don't need to be told twice that "Bison" is GNU's YACC implementation — the pun makes it instantly memorable.

One of my personal favourites is Ubuntu's version naming scheme. The "alliterative animal" form is highly memorable, and gives you two different words to latch on to, either of which is enough to uniquely identify a version. The fact they're alphabetical also makes it easy to check which version is newer (Letter collisions happen on a 13-year cycle, which makes it highly unlikely to be a source of confusion).