Yes, AmiUpdate does exist, and has been in development for the past two years and and off.
Currently, it is targetted at the OS4 beta test team, as the OS updates were easier to handle updates of.
Recently, there has been a push towards releasing it to a wider audience, and there are now quite a few 3rd party modules included in the update database.
You can see what is included by checking
http://www.amiupdate.net/dbcontents.htmlI'm currently trying to put togther a web site (html really isn't my thing) and once that is ready, the AmiUpdate situation will be reviewed.
I'd also like to get more applications on board working with AmiUpdate, but more information about that will be on the website.
If you have an application that can use the automatic updating capability, you can always mail me for more details.
Simon