Wouldn't surprise me if its name was from Budweiser's What's Up ad back during the last dotcom boom. It was really popular at the time.

https://www.youtube.com/watch?v=ZhlZoq3niIY

I always just kind of assumed the founder had a stroke while he was filling out the incorporation paperwork, but remembered it had something to do with "App"

and ICQ is "I seek you". Took years for my non-native English.