I've been creating something akin to Minecraft creative mode in the browser since 2016: https://github.com/alanszlosek/voxeling. It all started when I found the VoxelJS project. The possibilities really hooked me so I forked it, learned a ton about WebGL, then started my own repo and rewrote nearly everything from scratch. I've been having a blast. There are endless opportunities for optimization (must maintain 60fps!), which is extremely rewarding to me.
Last year I started making videos showing the code and the improvements I've made: https://www.youtube.com/playlist?list=PLGonE3T1sorRgdHNBGhpj...
That's just one of my projects, but the one I'm most proud of. Even if the code isn't conventional or pretty. :-)