I understand it may not be easy to narrow down the explanation, especially if you invested a lot of time and don't want to do a disservice to yourself by underselling it. Looking at the Tailscale tagline I quoted, it is small and ambiguous enough that it works marketing wise, regardless of all the features and solutions they offer. But it was just an example, I should maybe have used a totally different example of a product that is not in the same realm as yours.
The explanation you gave to me here is good but only because I vaguely know what all this jargon means. Try to think of a short simple sentence that a non-expert could understand.
I like where you are going with the graphics in the readme; I'd spend some effort on creating "intended usecase" scenarios, scenarios that highlight situations where the project is the perfect fit. Using a few of these to highlight very different applications give people a good mental map of where this project would fit well for them.
"John is looking for a way to provide access to an internal tool to work-from-home colleagues. This isn't simple to do because [...]. Octelium is a good fit because [...]. Here is how John would set it up: [...]"
I share some (very little) from some of the criticism regarding the clarity, but I disagree you need a tagine like Tailscale while your solution does several times more things.
Great product, im chewing through the docs already :)