Ah, internet buzz words....

First, a K2 application really consists of two different elements: the process that you design and the front end that allows users to interact with a process.

The process that runs within the K2 workflow engine has nothing to do with HTML5, CSS3, or whatever other fad might come along in the near (or distant) future.  A process will run regardless of any of these technologies.

The front end that users interact with can really be anything you want it to be: ASP.NET application, console application, SharePoint form, K2 SmartForms, etc., etc., etc.  It's impossible to answer your question in any meaningful manner because each of these is a) completely different, and b) constantly changing.

K2 SmartForms do a lot of things (not all) using some of the modern web technologies you mention.  SmartForms are activiely developed and so more new features are added with every release.

The View Workflow component of K2 is still Silverlight, but K2 is actively working on an HTML5 version of this component as well.

Hello

There is a blackpearl Compatibility Matrix on Help.K2.com for the different versions of K2. We also have release notes for the K2 products so should you need any information revolving around that Help.K2.com is your open resource.

Hope you're able to find what you're looking for!

Kind regards

Nelly