As I'm fairly new to open source (and there's a LOT of stuff out there), I have some ideas for what kinds of things we're lacking and should offer, but I don't know of any such apps by name. Maybe somebody does and can point me/us in the right direction.
1. Anti-malware. I like to leave a machine in a better state than I found it, especially if it's not mine. We have an antivirus program here (ClamWin) but a good antivirus should be complemented by (or include) an anti-malware solution. Something like Ad-Aware but that's not open source, so just something LIKE it.
2. System tuneup. CCleaner remains one of the most widely requested freeware apps for a reason. It's perfectly easy to run the portable version they offer and it integrates well with the PA menu (there's even a launcher up here) but everyone seems to prefer open source, so... what's open source's answer to CCleaner?
3. ID3 tag editing. We have a CD ripper (pretty sure we do anyway) and a few apps capable of playing apps. But what can edit ID3 tags themselves? I use MP3Tag at home; Winamp offers an editor built-in, but neither of those are open-source (AFAIK on the first one; I know Winamp isn't).
To reiterate, I am not requesting that these non-FOSS applications be made available at PA.com, but rather their hypothetical open-source counterparts, which I don't know the names of (or even if they exist, though, I'm sure for #3 at least, they do).