Drpepperfan wanted to make this thread but couldn't due to some weird bug. Anyway, post the things various sites have done for Easter April fools. This can include Easter eggs, site changes, redirects, etc.
Here's a few:
For our own awesome site, we had a sale on all entries! Bargain prices! Everything must go!
For April Fools, Google Maps had a Quest button that would transform the world map into a 8 bit style map with sprites of castles, shrubs etc. The street view was transformed into a pixelated and lack of colors view.
Over at Memebase, the mods accidentally changed the pH of the site, transforming it into MemeAcid. All front-paged posts that day had that weird text with tiny symbols coming of it.
The Ab-blocking add-on for Google Chrome instead of blocking ads, transformed them into cat images. Someone will be happy. I've heard that the developer is considering making it it's own separate add-on.
Imgur adopted the Giraffe as their new mascot. With the background of Imgur.com being a giraffe for the day.
MineCraft creator Notch launched the site marseffect.net advertsing his not fake upcoming game that's definitely not a parody of Mass Effect.
Post any others!