The Stream Ruby SDK by Stream allows to interact with the API to access activity stream and news feeds data. It contains installation and usage. Complete documentation is available at http://getstream.io/docs/
Three months after its initial launch, much-talked-about data portability service Gnip has released version 2.0 of its API, as well as the first glimpse of a business model. As we covered back in March, Gnip's goal is to "connect Data Consumers to Data Publishers in a low-latency, highly-scalable standards-based way." Gnip is a sort of proxy that makes data from diverse Publishers--services like Delicious or Twitter, which create activity content--available in a unified format, and notifies Consumers--like FriendFeed or Plaxo--via a push interface when new data is available. The new version of the API adds full data delivery, XMPP support, and advanced data filtering.
PubSubHubbub. Say that three times fast. If you're not familiar with PubSubHubbub, it's an extension of the RSS and Atom protocol that allows the feed to push content out when it's updated. That's just the sort of technology we should see from check-in APIs like Foursquare and Gowalla.