In addition to Living Social, which has just launched a local coupon effort, we’ve learned of  three other group coupon sites: Groupon, whose tagline is “collective buying power”;  Boston-based BuyWithMe, whose tag is “Let’s Get it, Together”; and What’s the Deal DC.

Groupon, the pioneer, is a 40-staffer, Chicago-based site launched by The Point, a company dedicated to collective activities, such as political fundraising. Its Chicago site was launched in November. It  is now available in 24 main cities and has 500,000 subscribers.  The site has 50,000 subs in D.C. alone.

The way it works is that subscribers just click “BUY” before the offer ends at midnight. If the minimum number of people sign up, they  get a printable gift certificate in their inbox that can be used whenever they get around to it. If not enough people join, charges aren’t processed.

What’s The Deal DC, meanwhile, has attracted 1,500 customers since its launch last month. Among other things, the five-person operation works with food bloggers to offer deals on recommended restaurants, and also throws sponsored happy hours with bar clients.