The frontend is built with Svelte. This was my first time using the framework and I found their website super helpful: https://svelte.dev/docs
Used Mapbox API and geolib (https://github.com/manuelbieh/geolib/) for building routes and for other geospatial tasks.
"Talkie" was built with simple-peer (https://github.com/feross/simple-peer) and WebRTC. Great tutorial can be found on MDN: https://developer.mozilla.org/en-US/docs/Web/Guide/API/WebRT...
On the backend I use Vercel's serverless functions which are mostly acting as trivial proxies for various open API's.
Feel free to email me if you need more info.