When someone new starts following me, I often wonder, "Who is this person?", quickly followed by "And how did they end up reading my updates?"

Looking at their brief profile, plus reading their updates, can give insight to the first one.

But knowing the answer to that latter question — the nature of your connections — can be tricky. Finding that one mutual acquaintance among the dozens, hundreds or even thousands of feeds they read, is like looking for the proverbial needle in a haystack.

Well, Twifter is a tool that lets you see whom you and another person both follow on Twitter.

Simple concept. Should be a feature of Twitter itself. But thanks to Twitter's savvy decision to offer an API, a third party was able to step up and fill that gap.

What's also cool about Twifter is that it's not limited to two people — you can see what three or more people are all following — and the interface couldn't be simpler.

And another cool use for the tool: find interesting users. Simply choose two users you dig, and then find out who they both feel are worth reading.