I frequently need to participate in international conference calls and find it frustrating to convert timezones when multiple countries/cities are involved, since most of the timezone converters require me to use drop down lists, search for zones etc.
Ideally I wanted a "free form" tool that lets me say "Dec 29 9:30pm pacific to paris,london,amsterdam" and poof it should show it to me.
Also, I wanted a mechanism where I can add "convenient codes" that make sense to me (like, say, "tx" is "CST6CDT", or "rockville" is "America/New_York") so I could keep my own shortcuts.
No program met my requirements, so I wrote my own in perl. This is actually a CGI program which needs to sit behind a local webserver. However, I've also provided a one click binary installer for windows which lets you run it from your desktop (uses the simple shttpd web server)
See Wiki for instructions
See here for source