https://github.com/Spark-Innovations/SC4
It's a bit dated at this point. It doesn't have a ratchet. I did implement one, but never got around to integrating it:
https://github.com/rongarret/ratchet-js
I also had an MVP iOS app which was never launched.
The reason I gave up on the project was that no one seemed to be interested. I spent several years looking for customers and collaborators and basically found nothing. The conclusion I came to is that a lot of people complain about the impending end of E2EE but very few people are actually willing to do anything about it except whine.
The connection between E2EE and privacy is to ephemeral to make that kind of judgment. If you live in the united states or similar country with a strong rule of law, the idea of paying for or using a specific E2EE app is functionally like asking somone to pay for free speech.
And even if it was more clear, privacy is like free speech in that you cant really measure enthusiasm for it in that way. Free speech and privacy are fundimental values that people dont want to pay for (for good reason!). But that does not mean they dont care.
People really do care about these things. And many many people will change how they vote and how they engage in civic action based on these principals. But asking someone to change how they live/communicate with others requires more then an intelectual "which party / candidate should I vote for?" kind of thing. For most people you need emotional investment for someone to overcome switching costs based on nothing but ethical / political principal.
As long as the harm to losing these core rights remains abstract you wont be to measure how much they care with metrics like that. Its a value that is too ephemeral and disconnected from day-to-day life to measure with a stick like "who will use this app".
But people can and do donate to groups like the EFF, and vote with their actual votes on this stuff. People really do care. Just like how people really do care about honesty, free speech, candor, trust, and other values of that sort. its just, you know, hard to measure.