Not quite an abandoned project, but if you want to be helpful, see if your local government publishes any data and do something helpful with it.

Here in Seattle, the OneBusAway bus tracker app was originally built as a side project, but is has substantially evolved into into its own company. https://github.com/OneBusAway

This project attempts to put a dollar value on car accidents: :http://seattlecollisions.timganter.io/collisions

Or this, which automatically scapes videos of city council meetings and transcribes the audio: https://github.com/OpenDataLiteracy/jksn-2017/tree/master/CD...