Glew, Glu, Glut and Glee. Which is used and when?

I’m having some issues with Glew in my 64bit Ubuntu openframeworks 0.74. I noticed that mine download of OF, the linux branch contains the **glew ** library
The master branche for 0.74 contains glew, **glu ** and glut
An older version I had previously built contains glee, **glu ** and glut.

My understanding is that all of these are some sort of wrapper for open GL. Presumably making it easier for developers to interact with low level openGL code through these libraries.

Why are different ones being used across different branches? And how does the openFrameworks libraries, particular the classes inside the gl folder know which one to use?

I get errors pertaining to glew from ofFbo however when I search this file all I find is references to gl rather than glew.

Regards.
Mitch