SpaceApi is as you guess an api to publish real-time data about your hackerspace. Mostly used to show if a space is open but can also be used for eg temperature, stock of Club-Mate, number of members now etc. For the api check SpaceApi website. Examples of implementing the SpaceApi interface.
- Hacker Hotel temporary switch easy to implement version.
- Fuz hackerspace based on esp8266 in a Sonoff S20 power plug
- Chaostreff-Potsdam SpaceSchalter
Do you have also a system but is not yet listed here? Please add it for inspiration for other spaces.