There have been some attempts at cooperative, non-profit and/or open-source ridesharing apps (notably in Austin), and some might still be operating. You are right that their challenge is the networks of drivers and riders. There's a trump card that we could play which would actually turn that into a strength against the competitive/for-profit/proprietary apps: #federation
! If all the alternatives (globally) federate with each other using something like ActivityPub, small groups in each town could #selforganise
to run driver collectives (teaming up to source/maintaining vehicles, insurance, healthcare benefits, etc), and devs could create any number of independent apps to innovate with better feature and UX - and every app would give you access to every driver or rider in the network!