"Util" is a library, in Limbo, with various commonly used functions. Some are in other standard libraries (like string.m, lists.m), others are not. This library was written because having to write these functions all the time (which is still faster than copy-pasting) is annoying.
The modules are named with a numerical suffix, a version number. Incompatible version of future libraries (e.g. with changed function definitions) will have a new number. This ensures existing programs using this library will not have to be modified after such an interface change.