It's free software https://github.com/steeve/xbmctorrent and uses libtorrent-rasterbar through https://github.com/steeve/libtorrent-go
Disclosure: I'm the author.
[1] https://news.ycombinator.com/item?id=7379166
I know the pi was created to be an educational tool, not a media device, but therein lies the problem.
It's free software https://github.com/steeve/xbmctorrent and uses libtorrent-rasterbar through https://github.com/steeve/libtorrent-go