For a variety of professionals, from designers to executives, the value of a good drawing and wireframing tool cannot be overstated.

Whether they’re used for producing user interface mock-ups or designing complex workflows and org charts, products like Omnigraffle, Mockingbird and literally dozens of others are available for quickly and efficiently creating such documents.

For those looking for a more collaborative tool, one option is LucidChart, a browser-based HTML5 Web app that lets you create charts, diagrams and wireframes with others in real-time.

Along the left hand side of the application lies a library of commonly-used shapes and UI elements, including some specific to UML, computer networking and iPhone user interface design. Across the top are your typical line-drawing tools and font options.

The real magic is in the app’s collaboration features. In real time, multiple people can make changes to a document and chat about it via instant message in the browser. Any changes made simultaneously are reconciled and merged automatically.

LucidChart looks and feels like a desktop application but operates 100% within the browser. Thanks to HTML5’s ability to cache content and data locally, the company announced this week that LucidChart now operates offline.

Obviously, changes made while offline cannot be collaborated on in real-time, but as soon as the machine is again connected to the Internet, LucidChart will sync your local changes with the latest version of the live document, reconciling them with any changes that have been made by others.

LucidChart, which is the Google Chrome Store’s top paid app, does offer a free account for up to two collaborators and 25 MB of storage. Plans for bigger teams in need of more space start at $25.

Want a professional account on LucidChart? The first five people to respond and give their email address in the comments will get one.