Free Domain Watcher?

I'm sure the title says it all, but is there any free script/software etc that can keep a look out for domain names and alert you when they are about to expire?

Thanks in advance.

edit: I dont know but there are services that you can "back order" a domain before its up for registration...in theory giving you the domain first..I recall some seeing type of war between the registrars over who actually has access to it first.