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7. CatBlock blocks ads with cats
Millions use AdBlock around the world to block annoying Flash and image-based advertisements on websites. For April Fools' Day, the creators of the popular Chrome and Safari plugin replaced ads with pictures of cats -- transforming some of the most popular sites on the Web with kitty-based imagery. But the prank was such so successful that it was spun out as a separate project and made available to the public.