More and more, drupal site builders have to make choices that they shouldn't if it comes to "choosing which contrib to use". We often can choose for an API - which is great - or choose for a ready-to-go module.
Heartbeat is an API that allows logging activity messages to the database. These logged messages are listed up to form a heartbeat stream. There are three built-in streams but developers can register their own.
I intend to write a module to integrate Hyves within drupal sites. Hyves is a facebook alike community website that offers an nice api, much like facebook does. Hyves is used by users in the Netherlands.