This isn’t a comprehensive list or anything, but more like my list of the sites I visit or ones that I found that happen to be participating. So let’s start the fooling!
NicoNico Douga goes monochrome.
Pixiv lost an I
Pangya Japan is celebrating its 5th anniversary by giving everyone white plates
Ragnarok Online Japan is rocking it out
Gizmodo Japan is sideways lolol
Otome game maker Icing Candy is releasing a gachimuchi C's magazine with a feature on how to make "boss dinner"
Otome game maker Amedeo makes a "futome" game, where all the eligible bishies...are actually fatties.
Otome game maker Sanctuary releases the furry version of Da Capo Girls' Symphony
Nitro+ releases a series of manequinns for cougars to 'play' with
Piapro has announced that Kasane Teto has become an official vocaloid.
Google Japan started a global shiritori service
Tsuburaya creates Tsubutta - a twitter service for Ultraman and his crew lol.
IREM Software makes a goofy game called "Seminalist Fantasia". Notice the long noses on everyone... xD
Someone made a lie twitter - a twitter for tweeting your lies on April Fool's day.
Geo Online made a section of their store dedicated to fujoshi.
A gachimuchi maid cafe opened up in Hiroshima
Japanese Opera browser page instead promotes boobies.
Caramel Box is releasing the movie for Otome wa Boku ni Koishiteru ww
FujiTV looks like google
Yahoo Japan is going 3D
Engan Bus service is now using a trap as its mascot
Xbox has a list of eligible bachelor/ettes for you to marry including the original Xbox, Bayonetta and Kasumi from Dead or Alive series
If the iTampon wasn't good enough for you, there's now a Plus version IPadL
The new DorarDVD player lets you watch movies in 4D. Just look at the difference...wait where have I...
There were a few others and you can find them over at Canned Dogs. Obviously there were more parodies than I listed but I figured ones that were not really interesting/unknown weren’t worth mentioning.