Is there a 'Mercurial Notifier' program that will tell me when an external repository has changed?

There are a few different tools for Subversion that run in the background, pinging the central repository every few minutes, and will alert you if any changes are detected (I'm using Windows 7, but th开发者_JAVA百科is is true for OS X and Linux as well).

Is there anything like that for Mercurial, that will watch a specific repository and alert me to any changes?

One way to do this is to have a local tool monitor the repository's RSS (or atom) feed. Every repo served over hgserve/hgweb/hgwebdir has feeds available and most systems have RSS poller widgets: https://superuser.com/questions/9929/rss-notification-in-system-tray

For example, for the main mercurial repository, you'd configure your feed poller to watch:

https://www.mercurial-scm.org/repo/hg/rss-log

There's an extension called NotifyExtension that is distributed with Mercurial that can be configured to send email when a repository changes.

Edited to add: If you prefer a local client solution, check out the Hg Commit Monitor.