There are pool tables and bright red vinyl booths at Diesel Cafe in Davis Square, both unusual things to have at a coffee shop. What’s not unusual, however, is the number of people that visit this coffee shop every day. Whether it’s Monday or Saturday, you’ll probably have a hard time finding a seat. But if you do, you can look forward to some good coffee and sandwiches like The Alternator, with roasted garlic hummus and tempeh bacon.