Jakandor was a cool concept that I never got around to actually using. Both the Knorrmen (barbarians) and Charonti (wizards) had interesting cultures The Knorrmen seemed to take a lot of inspiration from native Americans rather than "traditional" viking/Germanic barbarians, with many of them being part of "totem lodges" that had fighting techniques inspired by various animals, and with individual honor and accomplishment being paramount. The Charonti on their part had a very community-focused culture, to the point where they don't think twice about reanimating their dead so they can keep serving the community. In that way, they served as a way to present a Chaos vs Law conflict in a way that didn't involve cosmic forces. They also had an interesting twist where the Charonti, despite being the wizard-focused culture, had very limited spell lists – they were the remnants of a vast but fallen empire, and much knowledge had been lost in the fall and much of what they still had was segregated among different wizard guilds (matching the schools of magic).
But it probably suffered quite a bit from being a setting that deliberately cut out large parts of the core rules (e.g. races and some classes, not to mention using a highly curated monster list), and unlike Dark Sun which did the same didn't really replace it with anything. It was also an attempt at "culture gaming" in D&D, and that generally hasn't been D&D's strength.
en.wikipedia.org
