Edit: I'm looking more for the content released by companies not in the operating system/browser world. Sure, there's a ton of stuff out there from Microsoft, Apple, Mozilla, etc. about their UIs and how to build UIs for applications on those platforms, but I think there's more variety and potential novelty in the content released by other companies/apps. A good example in from the answers already submitted was Skype. It's more in line with what I'm looking for. It's more of a "here's 30 pages, in Issuu format, about how we should look", as opposed to, "here's 100pages of HCI guidelines, or a huge vault of developer documentation".
I think the content at http://ux.mailchimp.com/patterns and http://mailchimp.com/about/style-guide/ is an excellent way to solve some of the issues described on the landing page of the first link:
We’re also solving an internal communication problem by documenting and assembling a reference site of our patterns. A common lexicon of code and UI elements benefits us in a few ways:
- We can build consistently and focus on workflows and logic, not web forms and list items
- We can reuse code instead of roping in a developer
- We can maintain our code by seeing our patterns in one place, define elements in our application, and keep redundancy to a minimum
I'd like to review more of this type of content. Can anyone suggest other companies that have created and opened up this type content (and done a good job of it)?