Tech Stack
The following is a list of the technologies used per component of modmon.
Components
modmon-server
modmon-cli
modmon-ui
modmon-docs
Rationale
By nature, the creator of the project is a PHP developer. But not all devs have PHP installed and the ones that don't use it are less likely to try a project that uses it. Making any piece of modmon in PHP would require all devs to set up a PHP environment, which was seen as a barrier to entry. The upcoming official prefab/community recipe repository will be written in PHP/Laravel, however, and the "marketing" / .org site will be a Statamic site. Those will be fully open-sourced when they are stable.
On the other hand, almost every PHP dev has Node installed. So, Node was chosen as the primary platform for client-side development.
Go was chosen for the modmon-server backend, as it is a compiled language that is easy to install and run on any platform. It is very fast, and has a very small memory footprint. It has great integration with Docker, which is the primary use case for modmon-server.
Everything was chosen to be the best tool for the job, and the result is the current tech stack.