Twitter App Lists and Directories abound! I maintain my own list of Twitter apps of use for teaching and learning here
Oneforty.com recently opened its doors: "oneforty is your Twitter outfitter, with tons of resources for all things Twitter.
A recent Techcrunch postings yesterday has suggested a possible merger/acquisition with Twitter:
"We’ve heard an unconfirmed rumor that conversations are taking place between Twitter and Twitter-focused app marketplace oneforty. This is PURELY speculative and it’s unclear if talks are about a possible acquisition or a partnership".
Yesterday, Twitter however launched "A Very Unofficial Tweet Directory". A tweet from Twitter said "Help uncover all the awesome Twitter apps out there on #appwednesday".
You can find out what's been shared so far: here - and add your own!