When comparing Haiku vs TempleOS, the Slant community recommends Haiku for most people. In the question“What is the best operating system for a developer?” Haiku is ranked 6th while TempleOS is ranked 12th.
Ranked in these QuestionsQuestion Ranking
Pro Very Fast
Pro Beta has been released
After about 6 years since the alpha version, beta has been released on Fri, 2018-09-28. Check here for release notes.
Pro Only need 512mb ram
Pro Runs perfectly on old Hardware
Pro Allows you to talk to God
TempleOS comes with an oracle that lets you communicate directly with the Lord.
Pro Created by the smartest programmer that's ever lived
Terry Davis wrote the entire operating system, and the compiler for the language that the OS is written in, by himself.
Con No one uses it
It's a very niche OS that no one uses.
Con Small community
It is important when developing to be familiar with tools that other developers use. You can make any utility in any language you feel like, but if it's in an esoteric language that no one can read targeting a small platform that no one uses, then it was just something you did as a hobbyist, not as a developer.
This is not to say that Haiku isn't a great operating system to hack around on. Just don't delude yourself into thinking you're doing it to get familiar with tools that you need to know to be a better developer.
It's still in beta and quite unstable. Making it unsuitable for developing applications of any kind.
Con UI quite different to other OSes
Con Lead maintainer is dead
Terry Davis was hit by a train and it's unclear who will be taking over the project in his absence.