Ever heard of ACT! (exclamation point is part of it): http://www.act.com/?

Not sure they have a web app, but they are one of many popular software apps that accomplish what you are talking about. I remember having ACT! 2.0 in the mid-90s.

I'm looking at their site and I don't see a web app, though I'm not sure and I think it would absolutely crazy if they didn't.