The Great April Fools’ Webcomic Swap is arguably the oldest “community” event amongst webcomics. First held in 1999, the 2000 edition was also widely participated in. After these first two editions there was considerable debate over continuing the project (and some argued that with the event now lacking the element of surprise it was simply not much of an “April Fool” anymore).
The Nice, however, picked up the project and organized the Comic Swap for both 2001 and 2002. Syke announced recently that cartoonists associated with The Nice were planning on having the April Fools swap again this year (a tuesday if you’re curious).