For those who want full control, hosting your own server is the best route. You can run it on a free Oracle Cloud tier, a Raspberry Pi, or even your home PC.
This is a grey area. Eaglercraft does distribute Mojang’s assets (the actual game code was reverse-engineered; textures and sounds are often sourced from free equivalents or require you to own Minecraft). However, many servers require you to prove you own a Minecraft account. eaglercraft servers 1.8.8