Mmmmh, If the solution you are looking for leans more to 'configuration' than actual development, you could look at:
Microsoft's Windows SharePoint Services 3.0 (WSS)
Don't laugh ;)
It's a free technology (built using the .Net framework) that allows you to customise/control a 'hive' of sites/sub-sites, their membership and various content management aspects (document libraries etc) out of the box. Many many features such as RSS feeds, galleries, forums can be configured.
It also integrates with Office tools such as MS Word/excel etc (versioning and uploads/downloads).
It is good at collaboration type functions of teams, but could also be used as a CMS system for an internet site if so desired.
For example the authentication model can be custom (your own db) or use AD and can be exposed on the internet.
The sites can be skinned (20 skins out of box) or do your own/download Sharepoint designer skins.
WSS can be further extended using .Net , but you'll need a fair amount of WSS API knowledge if you want to tinker under the hood.
A great little app called SmartPart (http://weblogs.asp.net/jan/archive/2004/06/10/152932.aspx)
allows you to integrate your .Net .ascx files directly in a WSS webpart (So you should be able to roll your own custom webparts that integrate into the solution.