Screenhero engineer here, and currently working with CoScreen. TBH, Tuple adn Screen both seek to re-create Screenhero (and do an amazing job of that!) CoScreen, while using similar technology, has completely rethought the UI from the ground up, and is a huge step forward that the others are going to have a hard time catching up with. Instead of one person sharing their screen, with CoScreen, each participant can share individual windows into a shared environment that feels as natural as native windows. It's a fundamentally different vision for how to do remote collaboration.

Tech question: do you plug in to the native compositing UI system or do you have your own cross-platform UI compositing code?

We use a custom native compositor on both of the current supported operating systems.

What's your stack? Mostly C++?

I've heard the opposite advice.

Don't worry about competitors, worry about making your product the best it can possibly be (which if successful would be better than competitors).