If you’ve got something you want to get some feedback on, but don’t want to pay for a formal focus group:

The basic idea behind café testing is to situate yourself at a café, put up a sign to attract participants, and test the people that come to you. Because cafes appeal to a wide variety of individuals, and people at a café often have time to spare, café testing can be a great way to perform a quick litmus test in the marketplace.

Kind of like Rosa’s Coffee Tip.