nsec.app shouldn't require any servers, it runs in your browser. Or at least that's what I was told.
Discussion
I guess nostr:npub1xdtducdnjerex88gkg2qk2atsdlqsyxqaag4h05jmcpyspqt30wscmntxy runs both of these domains, which would explain why they’re down at the same time. I haven’t found the repo for nsec.app yet to try running it locally.
Then run it on a PC and you can access it from the browser of any device in your LAN.