Actually it is not that hard to create a better product than Skype. Skype sucks in so many ways that i wouldn't know where to beginn. Exchange developers, exchange the designer and the UI team. Hate it - but use it every single day.
I would also here some experts opinions on this.
How do they compare on a higher level. Say a RESTful API with JSON+HAL, HATEOAS approach, Versioning, etc. the full thing for a bigger usecase like Twitter, Tumblr, Facebook, etc.