I'm looking for a list of web-based prototyping tools and I'd like to build one up here by using StackExchange's democratic voting system.
There are already some lists around the web, notably these ones:
- Gui Prototyping Tools at c2.com -- this is a user-editable wiki
- Rapid Prototyping Tools at adaptivepath.com -- a list managed by the author of the article, who no longer works for Adaptive Path
I found both of those from the Google search "list of prototyping tools".
StackExchange UI should, on the long term, be the best format for managing such a list. Let's go for relevance, not necessarily completeness; completeness would involve adding tons of answers including little-known or outdated tools. Instead, I'd like to see a list of current web-based prototyping apps, and votes for each product would ideally evolve over time (eg. Balsamiq will likely start out at the top today, but 5 years from now we might see something else show up).
I'm making this a community wiki since it's more documentation than objectively answerable.