Reaktor instrument browser, designed for working with Reaktor 6 blocks. It doesn't work with instruments from older versions of Reaktor so don't try that. Maybe one day it will WHO KNOWS. Good luck out there champ. Hi.
Blocks showing up without an icon isn't a bug, it just means the block developer didn't add an icon. If you find a block that breaks or doesn't show up at all then please submit an issue to the ismsnoop repository.