What are some alternatives?
When comparing Doorbell.io and UserVoice, 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!
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
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Invision - Prototyping and collaboration for design teams
ZenDesk - Zendesk is a beautiful, lightweight help-desk solution.
UserEcho - Online customer support solution - Feedback Forum, Helpdesk (ticketing service), Knowledge Base and Live Chat by UserEcho