Popular private torrent tracker Bitsoup is currently open for signup. With over 100000 members and nearly 10000 torrents, Bitsoup is one of the larger private trackers out there. The site is currently open for signup but will close as soon as the max user limit reaches. This usually happens fairly quickly and open signups last only for fewhours if not minutes. If you plan to get in, see here for signup URLS and more information.
