DNN is described as 'provides a suite of solutions for creating rich, rewarding online experiences for customers, partners and employees. In addition to our commercial CMS and social community solutions, DNN is the steward of the DotNetNuke Open Source Project' and is an app in the Business & Commerce category. There are more than 25 alternatives to DNN for a variety of platforms, including Self-Hosted solutions, Online / Web-based, Windows, Linux and PHP. The best alternative is WordPress, which is both free and Open Source. Other great apps like DNN are Drupal (Free, Open Source), Joomla (Free, Open Source), ProcessWire (Free, Open Source) and Squarespace (Paid).
Create a beautiful website with no design or IT skills using the Rocketspark website builder. Enjoyably easy DIY web editing and ecommerce. Great for Designers and Graphic designers, manage your clients with the Rocketspark Studio.
BardCanvas is an Open Source CMS that fits perfectly for blogs/forums/social networks. It is fast (through several cache levels), heavily optimized (it wont collapse the server in high traffic conditions) and constantly improved.