Flock is a Web browser that's comes with social-networking features built-in. It uses the same rendering engine as Mozilla's Firefox, and can even install most Firefox add-ons. Where it stands apart is in letting users keep track of social activity on sites like Twitter, MySpace, Facebook, Flickr, and others in a sidebar that follows them no matter what site they're on. It's also got e-mail notifications, a photo uploader, and a built-in blog editing and publishing tool.
Flock is currently in its second major release, and runs on Windows and Macs.