At CrashSpace we have a publicly-viewable “sign” at https://crashspacela.com/sign/
to let members know when the space is open. This sign page is updated by a big button in the front room. Press it, the sign page updates, and you’ve promised to be in the space for an hour.
But last month, the button broke. So I made a new one based on an ESP8266 WiFi module, WS2812/Neopixel LEDs, and a custom PCB fabbed on an Othermill. Schematics, PCB & firmware at: https://github.com/todbot/crashspace-bigbutton