The three that I have found thus far are ODEM.IO, Blockchain.open.ac.uk, and BitDegree. But all are fairly underdeveloped and don't span into music tuition; the arts are always the last to be integrated it seems - I have lost so much work from music being 'last in, first out'.
If I do intend on developing an educational service, to a serious degree, I will put Musely on Steemit and see if it builds any traction. I would certainly have the time to blog about the foundational topics of music in order to teach those that are just starting out. I just have not the time nor the money in order to produce the standards I beleive such a project deserves.
RE: Musely: My Music Education Pipe Dream.