One minor improvement: the auto-selection of items by hovering the cursor could be a bit more visible - the dark grey is quite subtle (and not too different from black). May I suggest using a lighter color (or a classy red / orange)?
I think the similar problem exists in many areas and that's what stops people from moving away from Google and such - abscence of really cheap, simplified alternatives. For example, I wouldn't pay too much for the email, no matter how good it is. But I would pay 1€/month without a doubt. It's how we perceive the value of the product. No way the number of visitors of my humble blog is worth more than my cellphone data plan or my gym. But I realise that there are people who could say that analytics should cost more than a cup of coffee.
If may I ask, how long have you been working on these projects? do you have a full time job?
In case you didn't already know: using the same whiteboard on a 27" screen vs a mobile screen hides a big portion of it on mobile. It seems like the whiteboard isn't scaled according to the screen size.
Love the concept though!
EDIT: Never mind looks like if you just dezoom it works, my bad!
* https://onthesamepage.online/ - a minimalist private whiteboard with no registration; already used in German schools, but working on scaling it and prepare for a more general market.
* https://lalatabs.com - a tiny tabulature website for amateur musicians who can't read notes; need to add a few hundred songs and open it to the public. This won't be monitized, and will remain my little hobby.
* https://nullitics.com/stats/ - a zero-effort web analytics, easy to embed or self-host; much lighter and smaller than the alternatives, and as a result - much cheaper (I plan to charge 1€/month and that would still be profitable).