I'm taking the opportunity to write in the forum to "advertise" around my project.
I'm a regular but amateur user of Photo Mechanic and I was trying to use the keywords features.
I only found commercial catalogue for commercial purpose. Googling over I found one interesting project that sadly is pretty old and seems not maintained anymore.
Therefore I re started a project that I simply called OSKC standing for as you have already realize Open Source Keyword Catalogue.
You can find it here http://neiram44.github.com/OSKC/
I would need some help from you to contribute on this project. Github is not complicated (I'm not an expert) and enable easy collaboration.
But if you do not feel confident on Github you can contact me here and we will find another way to secure that you can contribute.
Thank you all for your help and interest