Chalkboard is a project my partner Abi and I started several months ago. Chalkboard is a collaborative tool for laying out software features, user stories, and screens in a way that is organized and communicative. Abi worked in web consulting with remote teams and wanted a tool that let him easily define project requirements with clients then hand the project off to designers/developers.
Chalkboard lets you quickly define software features / user stories and then create step-by-step user flows for them. User flows are linked up to application screens that you specify and can upload mockups for.
A lot of people have suggested we integrate/tie into Balsamiq. We have been talking about this since day one but have hesitated reaching out to them until we are 100% sure that this app can become a useful product.