There have been a lot of new socially based mashups showing up recently. In fact, we recently topped 700 social mashups. While many of these use the Facebook API or Twitter API, there are many more social APIs. The mashups below run the gamut, though, yes, also include Facebook.
Some Twitter users may have, at some point, had the need to share a conversation or a string of tweets with other people, and would have been left frustrated with the discovery that there wasn't really a way to do that. This was the very frustration that fuelled the creation of TweetVue; a tool that makes it possible to share Twitter conversations with other people. In addition, TweetVue's API gives developers access to this data, allowing them to access and share these conversations.