I realise that this is an extremely open question, so let me narrow it down a bit. I am toying with the idea of creating a membership site that could replace an existing Yahoo group.
I want to host the site, so that I control the data. Probably, an existing CMS could be a good starting point. The following features should be available:
- Member registration, authentication, etc (possibly using OpenID)
- Member profile pages
- Message board (this is a major feature, and must be well implemented)
- Photo gallery
- Files area
- A Wiki would be nice, but since that could probably be installed separately it is not a requirement
As these features are commonly available in a myriad of systems, I would like to give preference to the following parameters:
Good system design: I would prefer a system with fewer features and good system architecture to a bloated spagghetti monster with all the bells and whistles.
Easy to understand: This goes hand in hand with the previous point, but it is so important that I would like to give it a point of its own.
Easy to extend: Another aspect of "Good system design", but an important one to me.
ASP.NET MVC: It would be nice to work with a system that implements ASP.NET MVC "correctly", but I will definitely consider other platforms.