The Workflow Apps Alpha has officially started!
As said in the other post, you can access the docs via this url Alpha Docs.
What exactly are the steps you need to do?
1: Submit an App ( Read the first paragraph of Workflow Apps) - You may need to Request a Sandbox if you don’t have one already.
In order to Submit an App. You’ll need to understand the basics (which explain what the misc. urls you’re providing should return). Hop around the ALPHA sections of the docs until you have a basic understanding and/or follow the Quickstart
2: Wait for it to be approved. You will get an email when it’s ready. (This takes around 2 days 
)
3: Build!
During 1-3: Please post questions and/or feedback within this forum. For quick answers from myself and others, you can use the Slack channel! The invites are rolling out today.
We will meet later on to get more qualitative feedback. Until then, we’re trying to be fairly hands-off so we find the gaps in our docs.