Organizations such as the Brotherhood of the Rosy Cross, the Ancient Mystical Order Rosae Crucis, etc. did and do exist. The modern ones seem to be esoteric Masonic or quasi-Masonic fraternal orders or just magick correspondence course peddlers. Whether these have any relation to the "original" Rosicrucians of the 1614-1617 manifestos, and even whether the "original" organization actually existed is an open question. One theory is that the original manifestos were an elaborate prank or a call to form an organization like the one described in them - if either of those were the case, they succeeded admirably.

Either way, the Rosicrucians are a staple of conspiracist secret history, much like the Illuminati, the Knights Templars, etc. and it's inherently hard as hell to separate nonsense claims and rumors from verifiable fact about a secret society. Frances Yates did have a go in The Rosicrucian Enlightenment, although that is arguably more about the various mystic influences on the Enlightenment than the Rosicrucians per se.