I'd really like to run my own servers for some of the MMOs I played as a kid. But they're mostly from Taiwanese/Chinese/Japanese companies...

Does anybody have some resources on running your own custom servers? For example, how private WoW servers work, were they reverse engineering?

I've been following this community [0] which has unofficially relaunched a Korean online game which originally only lasted from 2003 to 2007 [1] and I played when I was a kid. It's amazing to be able to login into the same UI/UX and play the same game almost 15 years later.

[0] https://www.spgenerations.com/ [1] https://en.wikipedia.org/wiki/Survival_Project

The publishers usually can't publish their games' source code, because of various library and middleware dependencies which are not free or open-source.

Same issue with cheap IoT gizmos. Even if the retailers wanted to publish an implementation of their backend servers, they probably bought (rented) much of the functionality from a third party, under a license which forbids redistribution of the third party's IP.