The bot's name is obviously "Time zone bot". It utilizes the slash commands that are integrated nicely to Slack. You just start typing /... and it automatically lists you the available slash commands. For example with timezone bot you can type /convertTime 12PM GMT to PST EST CST. Or just start typing /conv.. and it will show you the available commands, no more need to remember the commands. I really like the way Slack has done the slash commands, both from the user side and developer side. The slash commands are super easy to integrate and use. Also great thing about the slash commands is that they have hints for what kinda parameters and in which order/format you should input them.
Time zone bot is also available for Discord and Telegram. The bots are pretty much identical, just the way of entering commands and some formatting is a bit different. Slack is a really big platform for real-time communication especially for work, and it's used by hundreds of thousands of teams daily. I think the time zone bot has some really nice productivity boosting features which will make it a good tool for all the teams and especially for international teams.