BitFactory is a general tracker specialized on german content. Everything on the homepage is german-only, so it is recommended that you understand german.
Currently it is invite only, but you can also donate 1,99€ with an SMS and get an invite code. They also have an invite request system where you can fill out an application and members can read through it and invite you if they like what they read. Their system automatically gives invite to the users. If invites are not used they will be shared with the other members. If you need an invite you can also ask the staff when you are "Power User".
Once you have your invite there are waiting times just like on e.g. Revolution-TT. Once you have uploaded 12GB and have an ratio of more than 0.9 they disappear.
This tracker is all about donating, because you can donate for just about anything. If you don't like the waiting times you can donate 1.99€ over the phone or with an SMS to get rid of them for one(!) torrent. You can also set a torrent upload only for one hour this way. Last but not least they have a "donate pool" where people get allowances at certain shops and for every sale with their Ref-Id all people who signed up for the donate pool share a certain amount of upload credit.
Their Homepage seems a bit buggy. It seems impossible to activate the "No XXX-Torrents" function, it has no effect for me. But these problems are only little things.
The last thing I want to talk about is a special rule they got: To give users with small upload bandwith a chance, everyone with an upload of more than 200kb/sec has to declare this and should not overseed.
They don't have a bonus system.
I could not find any statistics about how many users or torrents they got. Maybe someone can contribute this.
Their IRC channnel is on IceStarIRC (irc.icestarirc.org). Channel name is #bitfactory.
So here are a few pics: