For microblogging I think GNU social is a good replacement of Twitter. Due to federation and the different skins or themes available, people can choose to register in a node similar to twitter or in a node with different interface.

I closed my Twitter account and still microblog in GNU Social from quitter.se/larjona

I think pump.io is good replacement for 'general' social networks like G+ or Facebook. “Identi.ca” you cannot recommend it anymore: registrations are closed. Newcomers need to create their accounts in a different pump.io server. But that's a cosmetic detail only, decentralization in pump works as a charm, they can live in different server and follow our identica accounts without any problem.