One of the greatest things about Twitter is its open API that allows developers to build any kind of application they can imagine on top of the conversation platform. Twitter is famous for not having a lot of features, but when it does add one, it’s always right there with an API to accompany it.

My colleague Daniel Honigman wrote back in October about how brands can use Twitter lists. It’s a good post, and you should check it out, but I’m here now with the smartest use of Twitter lists I’ve ever seen.

It’s called ConversationList. In the past two weeks I’ve seen my name appear on a few of them so it seemed prudent to check it out. Which bring me to another of the greatest things about Twitter: conversations with smart people you’ve never met.

But how do you keep track of all the people you’ve recently conversed with on Twitter? That’s the obstacle ConversationList aims to overcome. It works by automatically building a Twitter list of those people you have sent @replies to recently. You can then track this list in TweetDeck or on Twitter.com.

Now when you reply to someone new that person’s tweets will be front and center for you, which should help give you a better idea of whether you would like to follow that person.

ConversationList isn’t perfect. It limits the list to the 25 most recent people you’ve replied to — I’d like to see that limit raised. But it’s smart, simple and useful.

Try it out — you can set it up in less than 60 seconds.