I have installed the optical design WB pyrate with the add-on manager. The add-on manager shows pyrate as installed and even updates it, but no pyrate WB option shows up in the WB drop-menu. Earlier, there was a discussion thread about the aesthetics of the pyrate logo, but I think my issue is different, so I decided to start a new thread. I am running FC 0.18, fully updated, on Ubuntu 16.04, as per the info below. I remember that earlier this year I had a similar issue with the WorkFeature WB not showing up as an option on both FC 0.18 and FC 0.17 while the add-on manager showed as installed, but that issue resolved itself.
OS: Ubuntu 16.04.5 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.15363 (Git)
Build type: Release
Branch: master
Hash: 9be3e633328335f1172456f5857219b7a08c70a5
Python version: 2.7.12
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)