They explain themselves like this:
Cyanite is an effective music search and tagging engine. Unlock the value of your music catalog.
Our artificial intelligence listens to millions of songs and categorizes them in minutes, so you can deliver the right music content regardless of the use case.
It seems - according to the screenshots - that they support tags like “Mood”, “Genre”, “BPM”, “Key” for example and they have some kind of similarity search.
Could this service be interesting for a cooperation with MusicBrainz?
(They also offer an API)