Here's one I remember: http://jgae.de/sdaeng.htm

From here: https://pajhome.org.uk/crypt/md5/uses.html#sdp

I used this many years ago, like literally 20 years ago. And it appears to have had a bounty! Maybe it is what you recall as well!

Once upon a time, 1password (macOS pwd manager) vault files could be opened standalone in a browser, which was extremely nifty.