CycleSync is free, and it stays free. I'm Bradley Clover, and I build it on my own.
Every room runs through a server that holds the queue, converts the music, hands it to each phone, and keeps the whole ride on one clock. That's a real bill every month, and as more rides use CycleSync I'll need a more capable and more expensive one. I'm not paid for any of this. Support covers the server and the time, and it's what keeps the app free.
Ride with it and tell me how it went. What broke is the most useful thing you can send: what drifted, what cut out, what phone it was on. What worked is worth hearing too, and if you get video of a ride with the speakers going, I'd like to see it. A review on Google Play, or a word to another ride organiser, reaches people I can't.
Email bradley@cyclesync.us.