So I built my own. Every engineering decision I've made is around keeping the operating costs very lean. I have no team, minimal server costs, and want to making virtual cycling more fun and accessible for anyone (regardless of budget).
It supports most indoor trainers, power meters, speed sensors, and hear rate monitors. There are many fun worlds to choose from and you can even import GPX files to make your own routes.
It's called OpenCycle: https://opencycle.net. Any and all feedback is welcome. Have fun!