What exactly "backend wallet server" should do? For database there's <a href='https://pouchdb.com'>https://pouchdb.com</a> and ElectrumX has support for websockets (<a href='https://electrumx.readthedocs.io/en/latest/environment.html#services'>https://electrumx.readthedocs.io/en/latest/environment.html#services</a>)
What exactly "backend wallet server" should do? For database there's <a href='https://pouchdb.com'>https://pouchdb.com</a> and ElectrumX has support for websockets (<a href='https://electrumx.readthedocs.io/en/latest/environment.html#services'>https://electrumx.readthedocs.io/en/latest/environment.html#services</a>)