Groupon is in the right battle - for small business, yet they are an army of old, low tech, type - sales people cold calling - which is extremely expensive and relatively low efficient.
The battlefield of the future belongs to drones. Like these mentioned stock exchanges - quick/real-time response, high volume, low cost, dominated by algorithms. In SMB/deals space it will be something like this - i get up, deciding to skip company cafeteria and go for lunch somewhere nearby, while walking through the hall press couple buttons on iPhone or whatever gadget, in a seconds the automated software of the local merchants (or the bored cashier if business is slow, though software is more plausible case and it would actually be outsourced, hosted Salesforce-style software contracted by the merchant) based on their discount strategies, current load, my status with them (if enabled/exists), etc... would respond with what they have, discounts, specials of the day, length of the line/crowdness, etc,... ie. the response is optimized for and reflects the current condition of the business, click - order if i want and they support pre-ordering, click - map, i'm getting into the car - drive.