foursquare2 is a Ruby wrapper for version 2 of the Foursquare API. Users will need to implement the OAuth2.0 gem as well, since the foursquare2 gem doesn't handle the API's OAuth 2.0 authentication flow.
Keek, social video network, recently announced the release of the Keek API. Alongside the API launch, Keek established a developer portal that includes tools and resources to assist developers in integrating Keek with third party applications. The Keek API grants developers access to public keeks (i.e. 36 second video updates), search, user profiles, klusters, and more.
Twitter yesterday announced updates to its developer platform terms that aim to reign in the use of automation by bad actors "to perform coordinated actions across multiple accounts." Twitter's updated policies forbid applications from posting identical content to multiple Twitter accounts.