Link Exchanges

I remember reading recently about a link exchange system that could help with link building. I'm thinking that effectively a blog would have lots of pages that can have links placed on the bottom, and that would be indexed etc. in google, and should earn you a link in return.

But I can for the life of me remember the name of the free exchange that was discussed.

Do these things work?

Do they conflict with and TOS like adsense?

As for adsense, I don't know, but I think link exchanges work, I mean direct ones, that's how I got my pr.