I have very little technical know-how, but Elgg has been recommended to me as a suitable tool for an idea that I have. I want to set something up called Let's Get DSSE (DO SOMETHING FOR SOMEONE ELSE)   

DSSE to be pronounced dizzy.

The idea is people post needs, help around the house, tuition requirements, lifts to appointments etc etc.  These requests would need to filter by locality. People would then respond, offering their service/skills for free, but the recipient would be required to make a donation, the amount entirely of their choosing, to a local project or good cause of the provider's choosing.

That's it in a nutshell, but there would be elements of sophistication that could be added over time. What I'm after in the first place is the simplest of models upon which to build.