Runtime Tools Kit (RTTK) is a package with a collection of units shared among some of my projects written in Free Pascal and Lazarus.There is not much of a coherency in RTTK beyond providing a place to place some code i want to avoid duplicating between projects and unless you want to build the source code of one of my applications that rely on RTTK you do not really have a reason to use this. In fact, the code is written over the span of several years (some bits are more than a decade old at the time of writing this) and its quality is sometimes questionable, other times it downright sucks.
Important: There is no documentation nor any API stability between releases (in fact, even if you decide to build the source code of one of my applications, if the application is old it may not compile out of the box).
You are expected to know how to use Lazarus and install custom packages. RTTK relies on the LazOpenGLContext package that comes with Lazarus as well as the fplilpackage package that is part of LIL. If the application you are trying to build does not use LIL you can simply rip out anything that references it from the RTTK package, there is not much unnecessary cross-dependency in it.
RTTK's license is zlib but keep in mind this note.