Meld is a visual diff and merge tool. It integrates with most version control systems. The diff viewer lets you edit files in place (diffs update dynamically), and a middle column shows detailed changes and allows merges. The margins show location of changes for easy browsing, and it also features a tabbed interface that allows you to open many diffs at once.
RhodeCode (formerly hg-app) is a Pylons framework based Mercurial repository browser/management with a built-in push/pull server and full text search. It works on http/https, has built-in permission/authentication (+ldap) features. It's similar to github or bitbucket, but it's supposed to run as a standalone hosted application and it focuses more on restricted access to repositories. It's powered by a VCS library that can handle many various version control systems.