farbot.com

Not long ago I stumbled across dijjer.org. It's an open source peer-to-peer system which relies on a java-based browser plugin.

The Dijjer setup is somewhat different from other peer-to-peer systems in that anyone can immediately put it to use on their site simply by prefacing any file link with a link to dijjer.org page, placing their own file's link as a parameter to that page.

When a user clicks that link, they go to the dijjer.org site to download the plugin, and once they have it, the dijjer plugin will start doing something similar to bittorrent -- caching file pieces and sending pieces of them between downloaders. The dijjer site runs the equivalent of the bittorrent tracker, but includes instructions on running your own tracker if you want to.

I thought it was interesting for a few of reasons. One, you don't need to run your own tracker; two, you can immediately get files into the system by changing the URL on your own server; and three, you can continue listing the file for HTTP download in the same location. The one downside, of course, is that dijjer is probably so unpopular that you're not likely to have many people running its plugin to share your file.