I know this has been discussed before, but I still haven't seen a useful portable bittorrent client to download. I know that you can make μTorrent portable, but its not open source (at least I don't think it is), and I haven't had much luck with deluge and anyway the one on this site is outdated. I found two useful bittorrent clients that do look promising. They are both portable already but I would like to see some one compile them into PortableApps.com format.
The First is G3 Torrent, the problem with this one is that the project was abandoned.
It is still a very good torrent client. It is written in Python.
The second is Halite, some people say download speeds are comparable to μTorrent.
I don't know why there is a x64 and x86 version, but x86 should work for all processors. It also has a set of 20 different languages. It is written in C++.