When people hear the word BitTorrent, they tend to leap to conclusions, some which are inevitably wrong. The fact is, the technology is used to distribute all sorts of content, including Linux distros and music and movies that artists and directors make available.
However, it is largely one of those keywords that sets off alarms bells with Apple, which keeps a tight rein on the content that appears within its iTunes app store. That's why it was a bit shocking when Blue Downloader made its debut.
With that said, Blue Downloader has managed to find its way past the restrictions, and is currently selling for $2.99 in the US iTunes app store.
The app initially avoided the restrictions that have thwarted others, mainly not mentioning the keyword "BitTorrent". In the initial release, restrictions applied. However, a recent update to the app opens things up a bit. The latest version actually allows access to Google, which enables users to search for all torrents on the web.
This could also be the undoing, of course. For now it's there, though it appears to be region restricted - my search reveals no evidence of it in the UK app store. It's also likely to not last long, given Apple's past policies on such things.
Update: The app has apparently been removed from the iTunes store.