The main difference is that Muddy automatically creates and updates those shared tabs for you based on what's being added to the project timeline (multiplayer feed of apps/websites).

We used some similar tools like Workona in the past but without constant maintenance, links would get stale and we'd abandon it. Wanted something that did that for us automatically.

(Also we support: website annotations, team presence, and letting you rewind a project's timeline back to any point in time)