NationBuilder - The world's first platform for leaders, handcrafted from scratch to help you grow your community and lead them to action.
UseResponse - Open-source, self-hosted customer feedback software, live chat and helpdesk system that you can install on your server. Organize documentation using knowledge base and get feedback from social networks with centralized system
Crowded Communities - The all-in-one community platform.
UserVoice - UserVoice integrates easy-to-use feedback, helpdesk, and knowledge base management tools in one platform that empowers users to speak and companies to understand.
FUEL CYCLE by Passenger - Think Passenger builds online platforms that allow brands to connect, create and communicate with key stakeholders.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.