I dont know about ready made applications but if you want to build your site is by using microsoft web developer express which is for designers who want to build dynamic web sites. Your site would have to be to include membership etc. The platform is asp.net 2.0 and you can use c# or visual basic. you dont need a great knowledge of programming knowledge as this application is very much wisywig.
the membership facility that is built into it is very easy to use. there are tutorials on how to use the application at the msdn developer centres. This is not the only application. Others may suggest open source php based apps. It maybe a good idea to look around first.