These were quite popular as a startup idea once. I remember Gravitricity (now defunct) being posted here: https://news.ycombinator.com/item?id=24414497 https://

These were quite popular as a startup idea once. I remember Gravitricity (now defunct) being posted here: https://news.ycombinator.com/item?id=24414497 https://news.ycombinator.com/item?id=24414497