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 doesn't show up at all then please submit an issue.
I don't own an OSX computer so if you're a cool hipster OSX developer and are familiar with JUCE please configure a build and submit a pull request thanks.