Respond, previously Respondly, is a social customer service and community engagement tool, built by the team at Buffer. It allows you to monitor your Twitter account(s) for @mentions, DMs, and even search keywords like #hashtags all from an inbox-style interface.

 
On top of this, with Respond Pro, collaboration features like Assigning and Double-Tweet Prevention make it easy to work as a team with colleagues to tackle those conversations together.