ZoneStamp is a timezone converter for online events. It's simple and easy to use. Zonestamp is currently maintained and run by Derk-Jan Hartman but was orginally conceived and written by Raquel M. Smith. The current version runs at https://zonestamp.toolforge.org.
If you run online events with an audience located across different timezones, ZoneStamp makes it easy to create a "Stamp" for the date and time the event will be happening, then send the link for that stamp to your audience. When clicked, the ZoneStamp will automatically show the user what time the event will be happening in their timezone.
ZoneStamp is great for emails - instead of listing three different timezones that don't cover your whole audience, just list one and provide the link to the Stamp.
Also, it's free! Thanks for using ZoneStamp!