LETSystems
See
http://www.gmlets.u-net.com/design/home.html
for an overview and
http://www.gmlets.u-net.com/ for more info.
Timelets:
In the overview they use national currency as
measurement for value.
But I think it would be mush better to use
time for this.
If I need a friend to help me for 2.5 hours,
I could just pay him 2.5 hours in timelets.
This would also prevent inflation and make it global acceptable.