Hello! You have stumbled upon my little calender app. It's designed for friends to coordinate when they have free time for doing some event or activity.
You can:
This software is written in php and plain javascript, with no dependencies. You can self-host it, if you want. For more details check out the source code!
PS: I've been informed that a similar tool already exists. So if you want the same idea, but 15 years old, closed source, riddled with ads and made by someone more professional than me, consider checking out when2meet.com.