I have some ideas for p2p apps. I think it would be cool if I could tell a p2p app not to download files that I've already downloaded before.

Sometimes I download a file, delete it because I don't like it, and download another file with the same content because it is named different and I wasn't able to tell right away.

To avoid this, the p2p app, for example, could denote that some search results have already been downloaded beforehand, or eliminate those files from the search result altogether.

Another idea I had was sharing user ratings of files. Each user gets to share their evaluation of files, and those ratings are are collected and averaged by clients. This information could be used to avoid too much spam / poor content on the network. The ratings could be as simple as a thumbs-up or a thumbs-down per file.

Another idea I had was that mp3 files would be matched by hash of audio content, excluding id3 tags. This would allow swarming on the audio content of two files even if they have different tags.

Also, a simple closed p2p network amongst known friends (esp. just two members) would be nice sometimes, because not every content is appropriate for the public to see, and currently I have trouble spotting my friend's files when we are running the same p2p app.

It would be nice if my p2p app would alert me of duplicate files in my library. Duplicates would be detected by hashes.

Hope these ideas aren't all redundant.