What are some alternatives?
When comparing Doorbell.io and Bizpopuli, you can also consider the following products
UserSnap - Usersnap Track is your central place to organize user feedback and collect bug reports. One screenshot is all it takes. Get rid of endless email exchanges and coffee-stained sticky notes. Your new life is awaiting you!
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.
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
UserEcho - Online customer support solution - Feedback Forum, Helpdesk (ticketing service), Knowledge Base and Live Chat by UserEcho
Invision - Prototyping and collaboration for design teams
idea.informer - Idea Informer is a idea forum similar to uservoice or getsatisfaction.