@Corno_1, utillib is just one of the collection:
utillib.lua : module containing utility functions that are useful in any script, for example PlayerLookingAt.
quatlib.lua : module for doing Quaternion based stuff - not for the faint hearted.
physlib.lua : module containing physics related functions - see tutorial on scripts forum for details.
Those three are included with GG, also available (again check out the script forum) is
textlib.lua : contains functions that allow 'font' sprites to be used, mainly because GGs font handling is pants.
Currently being worked on and will be released when done:
zonelib.lua : my old zones script converted to a library module, allows named zones to be created from waypoints and provides functions to detect when the player or any entity enter a zone or exit a zone etc.
ailib.lua : a library of functions related to AI manipulation, what this one will provide is still to be determined.
I may convert a few more of my scripts to libraries, for example the vehicle related stuff and my old ezentitymover script which is crying out for conversion when I have the time. Also on the plate (but a bit up in the air since Lee mentioned something about a 'new' particles system) is a particles library to simplify the use of particles.
If I ever manage to finish that lot I have plans for a HUD library and a map display library.
Oh and as if I'm not already as busy as a one-armed-decorator I intend to revisit the whole inventory/survival genre with a library full of general purpose functions related to the implementation of said genre.
I've probably forgotten a few things as well.
Been there, done that, got all the T-Shirts!