It is an incredibly complex piece of software. Where / how did you learn how to write this? Did you write it all yourself or is it based on snippets from elsewhere?
I am an original author, but now it is not just me - other engineers from our team work on it. Drivers, TCP/IP stack, TLS stack, protocol handlers, good reference projects and docs - there's plenty of stuff todo.
It is not based on anything, written from scratch and rewritten several times since 2004. The only pieces of 3rd party code that we use are crypto algorithms. We don't reinvent those, just take stuff written by others under a public domain license.
It started very simple, as a web server for the Web UI, and then gradually evolved over the years.
Network programming, and especially embedded network programming, is difficult. Now our team works on a tool that is going to work like grafana. A simple configuration wizard, and a simple UI constructor should give a possibility to create sophisticated Web UI and other network functionality (like, remote control over MQTT) by simple point / click / configure - and we'll generate the working (mongoose-based) code. Anyone, even non-experienced developers, should be able to create descent implementations with little effort. That's our goal.