Still nobody is financing this, so the dev fees are still there and this is still not open source (will be removed and become open source if the equivalent of 5 BTCs is reached), but here is the offline standalone version inside browsers :
https://peersm.com/walletThe code is loaded once with one request (including the data-uri image, so the design is a bit succinct) and is sandboxed so nothing can leak/be easily accessed even from the browser console, it can be checked using the check code button and comparing with a third party (here github, if some people want to host it also, they are welcome), this button can be installed as a bookmarklet for future uses/checks
It is highly recommended to use the advanced mode offline, the tool will advise if this is not the case
Of course this is not sending anything outside, not using tracking stuff, neither browser storage or whatever insecure feature
It can be used with the Tor Browser if you activate javascript
This is a kind of bitcoin-cli outside of bitcoin core for different coins, it could be extended for Lightning and other use