A website where you can browse between startup seeking money and have the possibility to fund them yourself. For instance, startup X might need 50 000$ . You could give them from 1$ to 50 000$ if you think the startup would be a success. Of course, there would be a way to give back the money if the startup is really a success. It might be a part of the company (such as 50 000$ = 5%), or a simple: 1$ now will worth (1$ + x) in 1 year.
Does is already exist?