A little interactive explorer for the CIE HLC colorspace, which has been suggested (by the freiefarbe.de people among others) as colorimetrically sound colorspace that's also well suited for communication.
— Raph
Xi (pronounced "Zigh") is cross platform, but it has a native UI on every operating system that it runs on. Text is rendered on the GPU, so it's blazing fast.
— davidbalbert