Love this idea, especially on the heels of the most recent episode of "Last Week Tonight with John Oliver" where he talks about food waste. This is a great variation on the potluck dinners my friends would hold, when we were all just out of school and living in Chicago. A good target market to beta test this would be near a college campus with a strong off-campus housing community, or anywhere with an existing common social network in close-proximity, where the options for "home-cooked" food are limited. Once a database of offered menus starts to develop, you could offer suggestions to cooks based on previously submitted menus, or a "tips for working with (fill in the produce)." This might be especially helpful for ingredients that are less common.
Loving all the gamification ideas, especially the ones that mention coupons or rewards. Made me wonder if there was a way to earn points like a credit card, which could be exchanged for things like gift cards. Then you'd have the idea of accumulation of points over a longer period time, which would encourage the development of habits (Someone once told me you had to do something every day for 28 days to make something a habit--I did this with flossing, and I can vouch that it does in fact work). You could have double points for certain activities or milestones. OR...much like McDonald's popular Monopoly game, you could earn badges or game pieces, randomly generated, that could be collected on a virtual game board towards earning larger rewards. The tricky part is how to make sure people are inputting information honestly. Combining with an app that tracks GPS would be pretty straightforward, but what about people who do yoga in their own homes?