If it is for themes and plugins then a 'club' type setup - Something like WooThemes - There stuff is (possibly was) all open source - They tried to keep that a bit of a secret and you joined a 'premium' club with support and access to extra bonuses etc - It is set up in such a way it seems like you are buying the theme...
Lots of sites do it.....
Here is a good link:
http://wordpress.org/themes/commercial/