Thanks for asking. Yes, its somewhat similar (IMO, as similar as facebook vs Twitter). Meetup is pretty close though - the core philosophy of meetup is you want to plan ahead and find people of similar interests. you need to have a continuous meeting groups. Its a big overhead and not a simple task to lets say conduct a garage sale or find a buddy for running around a park.

I would say tellStreet is more like twitter whereas, others are more like email groups.