There are a lot of virtually-identical web clients for Twitter out there, but Philtro is a new one with a unique approach. It uses a system that you're probably familiar with from email spam filters to weed out the irrelevant stuff and show you the posts from your Twitter stream that are most interesting to you. There's a thumbs-up/thumbs-down rating system that trains the filter and lets you correct any mistakes it makes.

It's definitely an original approach, but there's already a way of weeding out spam on Twitter: just follow the people who are relevant to you. If they're not, then don't follow them. If it gets to the point where you're following so many people that the small percentage of irrelevant posts from otherwise-relevant people adds up to more than you can handle, consider dropping some people. On the other hand, if you're a business user of Twitter, or a "social media marketing guru" of some kind, Philtro could prove indispensible. Philtro does have an audience, though: according to their blog, their average user only cares about 5% of the tweets they read.