App.net was originally Mixed Media Labs, which made a product called PicPlz. They took over $7MM in funding. I _thought_ they got funded from YC, but can't find a reference to this now, so I must be mis-remembering.
http://www.crunchbase.com/product/picplz
http://www.crunchbase.com/company/mixed-media-labs
They then shuttered their product to build App.net, doing the whole 'crowdsourcing' thing and collecting another $500,000. You know, which throws that whole "We won't shut down, you can build on our platform" thing into some amount of doubt.