If you're reading this, you're probably interested in social media and/or how showbiz is changing coz of the Internet. If you're not into that stuff, this is gonna get pretty boring. (Casual Spreadsheets is all about social media and post-Internet showbiz, baby!)
Casual Spreadsheets is a sloppy side project dedicated to sharing the little documents many of us make for ourselves/our co-workers. It began with a tweet. Then more spreadsheets got shared. Requests came in, Some people said, "Hey, I use this in my powerpoint, I'd pay for this!" Their bluff was called, and now you can pay for a subscripton, too.
Almost everything here is free/public. But paid users get some bells and whistles, exclusive access to some sheets, and warm feeling in their heart knowing they're helping keep endangered spreadsheets around.
Casual Spreadsheets is built on a rickety system of rubberbands, Google Spreadsheets, Github, ugly code, and spare time. You probably shouldn't depend on it for anything too important.
Go check out the "Popular" tab. There you can find the spreadsheet that started it all.