Update: Twitter announced today at its Chirp Developer Conference that it has 100,000 registered apps.

Original Article: Since its inception, one of the biggest knocks against Twitter has been that it's been hard to figure out what to use it for. As time has gone by, this has become much more clear to a great many people, but you can rest assured, there are still plenty out there who have a hard time justifying its use. Others, particularly in the business world feel like they need to be using it, but still have a hard time finding ways in which it can be most effective and beneficial to their specific needs.

What Twitter apps make Twitter more useful to you? Tell us here.

Twitter's usefulness more often than not, becomes much more apparent when you find that app that frames it in a way that makes sense to your life or your business (or both).

There are at least 10,000 Ways to Use Twitter.

OneForty is a directory of Twitter apps, that's been around since last year, when we first discussed it with founder Laura Fitton. Last month at SXSW in Austin, we dropped by Fitton's party (which featured some fantastic beer, I must say) and talked with her about the site, and the vast array of Twitter tools that are constantly being developed.

At the time, Fitton said OneForty was up to about 2,500 Twitter apps, and that they've found "evidence" of 7,500 apps more. So that's about 10,000 apps out there providing ways to use Twitter, if this is accurate. There's got to be some useful ones (might I suggest our own Twellow - the Yellow Pages for Twitter). Currently, the site claims, "2,624 Twitter tools that make Twitter more useful for your business, career or life."

The directory has 23 main app categories from Advertising, Analytics, Blogging Tools, Business, Email, and Search, to Mobile, Shopping, Productivity, News, Networking, and Monitoring (there are plenty of other more fun ones as well, like Games, Music, and Multimedia).

Any business evaluating their social media strategy, and Twitter strategy in particular, would probably do well to take some time and do some Twitter app exploration. It's entirely possible that there are apps out there that will have a profound impact on how your business interacts with Twitter, and could potentially have a significant impact on your online strategy as a whole. OneForty is not the only Twitter directory out there, but it's certainly a good place to start exploring.

What Twitter apps do you use for your business? Share your favorites here.