Certainly Google App Engine(Phyton). It is nice to have a small free version for experiments and own projects. Great way to get your hands dirty. AWS/Amazon has

Certainly Google App Engine(Phyton). It is nice to have a small free version for experiments and own projects. Great way to get your hands dirty. AWS/Amazon has to do its homework and open up a sandbox type of platform where you can put your small project of your own at no cost, and opt-in that others can copy/improve. 'Open' is the best way to innovate (small steps of improvement) on something. Zynga (the company and the concept) proved to be successful with enough leverage and network effects Facebook provided.