All the backends (git infrastructure, game engine, game scheduling, ...) are written in Golang.
The game engine includes collisions detections, agent physics, visualization rendering, projectiles, ...
We have our own message broker system written in Nodejs (which suffer from performance issues). We are planning to re-write it in Golang or use a solution like Apache Kafka.
The visualization of the arena in 3D is made with BabylonJS and written in TypeScript.
We use HAProxy extensively to handle all the traffic from the outside as well as internal inter-service communications, TLS termination, load balancing and security.
All the services are running in Docker containers and deployment/orchestration is done using Ansible.
The website is written in PHP, we used the Symfony framework.
GraphQL is used internally to exchange data between services.
We used mainly Golang for performance reasons.