The Open Mic is open to anyone and everyone (though it's mainly musicians who play). Trof have 3 mics and 3 DI boxes (for plugging in guitars etc). It can tend to get rather busy, so get there as early as you can (all the slots tend to go by 9pm-ish!)
The slots are long enough to play 2-3 songs, about 15 mins each on stage. The audience is really supportive and it's usually milling, with a wide mix of people (musicians and non-musicians) in the audience.
Trof, 8 Thomas St. Manchester. M4 1EU