Ask HN: Cross-platform open-source app for meetups with existing friends?

I'm currently reading Stolen Focus by Johann Hari and it mentions "What if Facebook had a button to indicate you were open to meeting up with some friends today/this week, and matched you with your other friends that indicated the same?".

I'd be very interested in a no-frills app that provided this functionality in some form - no-frills as in no advertising, no incentive to keep me looking at the app other than for the stated functionality, no chat functionality (I already have ways to message people), no monetisation. Maybe some tools for geolocation since I have friends in different cities.

I'm a bit introverted, and so often go long stretches of time forgetting to reach out to people to organise things - feels like this would be a tool to broadcast "I'd like to meet-up this week if anyone else would!" to reduce that which would otherwise need to be 1:1 messages to individual friends/groups.

I tried searching the Play store and google for similar functionality, but all I kept coming across were apps for finding/meeting new friends, generally all run by for-profit companies.

It's something I'd be interested in creating, but would rather just use if it already exists. Would appreciate if the HN hive-mind can pull something out of the haystack?