Some time ago, I was playing indoor with a group at a local indoor arena. The system they used—five minute games with teams shuttling in and out—worked quite well. Our games were very popular but we had trouble finding times. Casual soccer games are always pretty hard to set up. People work different schedules, there are often weather issues if you're outside and if there's money involved, how do you keep track of who has paid and who hasn't? I believe there should be places where players can show up and play whenever they want.
Originally, this was an exercise to keep my mind from turning to mush after retirement. But as the idea developed, I was able to make working models of most of the components and connect everything together. It's now able to demonstrate complete games—on a small scale of course. I've shown the system at several Maker Faires. Most people seem to see it as a nifty collection of LCD screens and flashing lights but folks who play recreational soccer understand it immediately and get very excited. There definitely seems to be a demand for a way to play soccer whenever you want.
The system runs Ubuntu Linux, is programmed in python, and communicates to the various modules through RS485. It detects goals using piezo sensors. There were many options with more advanced technologies but the simplest solution always turned out to be best.