Our new IT system is really great – fast, easy-to-use and it is even beautifully designed. It’s the bee’s knees (das Größte / Beste)
This idiom changed from its original meaning (which was „small“ – quite logical) to its current meaning in the 1920s. It was fashionable in the US at the time to create nonsense slang. There was a whole collection of similar phrases, all of which meant „something excellent“: tiger’s spots, bullfrog’s beard, elephant’s instep, caterpillar’s kimono, turtle’s neck, duck’s quack, duck’s nuts, monkey’s eyebrows, gnat’s elbows, oyster’s earrings …
The bee’s knees was similar in structure to these phrases, and so took on this new meaning. While most of these phrases are no longer in use, one of the others is still with us – the cat’s whiskers.