I used to always have to go look up how to convert dates to and from UNIX format. I still would, if I hadn’t made this little Excel spreadsheet that does it for me.
Whenever I need to bring a date in or out of UNIX format (especially for LDAP filters) I use this little spreadsheet. It wasn’t worth the effort of making an app, or even a web app to do. I hardly ever use it, but when I do I’m glad I have this around!