Buttercup developer here:
Really nice to see such a broad discussion going on - and thanks for the article!
Just to chime in: What we're doing with Buttercup is trying to make an application that we want to use, and are proud to introduce to our friends and colleagues. We care about usability and security - and while we're not going to nail these upfront, our project is open source to help us deal with them.
On the usability front, we want our software to run on every platform and be easy to understand. This also means it has to perform well - we take any lag concerns seriously, and we've honestly seen little to no concern on the subject of using Electron for an application base.
On the security front, we haven't invented any of our own crypto, and rely heavily on the tried & true built-in methods on each platform. We use crypto built into the browser in the browser extension, c-based crypto methods from within nodejs in the desktop app, and built-in native crypto methods on mobile.
We're also planning to release our mobile application very soon!
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