Terraeconomicus is a group of islands (regions) that I maintain in Second Life to teach and do research on virtual worlds.
EconWillow is a toolkit for running economics experiments in Python and HTML. It was written by Jaap Weel, one of my graduate students who ended up working for Facebook. The willow API makes it easy to create a subject interface on a webpage and network together many subjects into a single networked experiment. The manual for EconWillow can be downloaded here.