The majority of people cannot easily turn a few hours of their time on a whim into money because most of their working life is pre-scheduled. Others especially those most likely to be able to pick up a shift aren't paid all that much. I find that ANY new software requires spending time learning in addition to any cost up front. Furthermore most of the paid software would require me to use a worse OS and pay for the privilege so its an awfully hard sell to bother.

As far as accounting software I who simply manage my wages haven't ever needed anything more complicated than a spreadsheet. What software I've seen is kind of obnoxious and terrible so maybe this is an opportunity for someone.