Hmmm? This is a tough one because your product is so wonderfully horizontal, meaning it applies to a very broad set of cases. I'd slice and dice in two directions.

First, I'd think about the general process of collaboration on a document, for example: a) drafting - are two people actually writing the words together? I personally don't like this. b) first read through together staying on the same sentence or page, c) editing together, etc.

Second, I'd think about industries or verticals or contexts, such as in a Legal setting, in a Tech Documentation setting, in a coding or XP dual programming setting, in a social media post drafting setting, and so forth.

Check out: https://medium.com/look-what-i-made/fd48c3b412bc Seems to be evocative of what you're doing, but targeted to one specific use case of "pair programming".

I'd suggest:

1. Looking at different industry verticals where a truly synchronized viewing of documents is of use
2. Then arrange those in a descending order using a mix of variables such as size of market, perception of pain felt by client, etc.
3. For the verticals that come out among the top 3-4, it might make sense to do another round of customer development interviews to validate your hypotheses around utility to customer

This could potentially point you to a small number of compelling use cases.

I'd be happy to look at (a) what use cases you currently have and (b) brainstorm/be a devil's advocate as you go through the process above.

To find out how to describe your use case, I would get real users to use your product, then ask them "How would you describe this product to others" or "If you were to recommend this to a friend, when would you recommend a friend used this?"

Do this with 10 pairs of people (one presenting and one watching) and ask them the above questions. I guarantee that you will learn the answer to your question.

For me as a user, your landing page is confusing to me. When reading at the top I was assuming this was to be used when two people are meeting remotely, kind of like a skype + screen share replacement. Then in your graphics you show two people standing next to each other. So I would be talking to my co worker and also controlling her screen.

As this is in Lean section : what is your value hypothesis?