It is partially based on an old flash game I used to love called "Cheese Dreams".
This is a surprisingly old idea of mine, I started working on this in 2016 and worked on it for a year, back when the "agar.io" craze was happening, sadly, the project got very bloated quickly and hard to maintain. Also, the server and client were completely different software, leading there to be inconsistencies in the physics simulations on both sides. I decided to restart from scratch with this project, focusing on having most of the code in a unified "base" project.
The hardest part is keeping real time planet physics feel right with latency on a network connection. Alone, real-time networking games can be simple to make, and planet gravity systems can be simple to create, but when together, things get pretty complex.
Right now, I am still having some inconsistencies, even when they are running on identical code, so I think there are now floating point errors causing issues.
The library I am using for Java allows you to export to WebGL, and I am using web-sockets for client-server communication, so that is the long-term plan.