The only thing missing from the list of applications that I use occasionally is a bittorrent client. I'd suggest Deluge, as it's both full-featured, lightweight, and open source.
EDIT: Oh hey, look, it's in the test release section. Never mind.
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We have Frostwire. You can find it here
https://portableapps.com/node/11822
It seems pretty popular and though I haven't used it yet it looks good to me.
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Deluge development test is here:
https://portableapps.com/node/12115
I don't particularly care for Deluge but a lot of others seem to like it. Give it a try.
I know it's not open source, so it couldn't be released from here, but if you just want a program to USE, probably the best portable bittorent client IMO is utorrent. Just put the standalone .exe on your USB stick and create a blank file called settings.dat in the same folder (if you don't make the settings file it tries to "install" itself *read: copy itself to the program folder* but otherwise it DOES work without installation at all). Voila. You could even put it onto the PortableApps launchpad too. It doesn't write to the registry or anything. Plus, utorrent 1.8 supports relative paths, which makes it entirely portable, so far as i've been able to tell.
...oh, and it's reeeally lightweight too (I think the .exe is 261kb)
Quamquam omniam nescio, nec nihil scio.
Check the beta forum. I've posted my launcher for uTorrent 1.8.