Date and Time Toolbox (link)

This webapp has three tabs. The first is a date diff calculator with some advanced features like counting the number of workdays beetween two dates, including Hungarian public holidays and Saturday workdays.
The second tab is a countdown timer. The timer can be shared with a link. Every browser with the same link is synchronized to the master timer.
The third tab helps you practicing the Doomsday algorithm and figuring out, which day is 21 December this year for example.

Features:

• interactive (all calculation is done in the browser)
• check if the computer's clock is accurate
• date diff
• timezone conversion
• converting from and to unix timestamp
• Hungarian public holidays and Saturday workdays back to 2007
• sharable countdown timer
• call a webhook when the time is over
• notification when the time is over
• Doomsday algorithm practice

Technology:

• React
• Typescript
• MomentJs
• Pubnub (publish-subscribe service)
• Bootstrap