If you mean just one-off jobs I don't think I've personally heard of anything like that. I think most companies wouldn't want to touch that mostly because it'd likely lead to poor quality, undocumented code that can't be maintained since nobody within the company wrote it or is in the loop on it. And that'd only work for small, self-contained projects. You can't really do contract work like that contributing to larger codebases because it'd take too long to familiarize random new people with a complex existing codebase. By that point you might as well just hire them, even if as a contractor.
Maybe something similar, you might be able to find open source projects where people are willing to pay money to have a certain feature developed in the program. I run into stuff like that now and again. But AFAIK there isn't much "gig" work in the programming world.
Disclaimer: not a professional/career programmer.