Follow and be followed
Every time you use Twit Pro Quo, it will make you follow at least 10 new people. Hopefully, a few of these 10 in turn will follow you back.
As described by the authors,
When you use our service, you are added to the site’s queue. This is basically the line of people who used our service before you got here. Each person who uses our site stays in the queue until they have gained 10 new followers from us, and then they are removed. There is no limit to how many times you can use our service, however, you cannot use it if you are currently in the queue (you’ll need to wait). On that note, we provide you with the option of entering your email address so that we can alert you once you’ve gained 10 new followers from the queue (and can then use our service again).
The video below describes Twit Pro Quo,