Runtime Tools Kit is a Lazarus package that provides some common units for Runtime Legend tools. These units provide functionality such as logging, mesh loading, 3D-related math (vectors, matrices, planes, etc), texture loading/handling, etc.
Runtime World makes use of the Runtime Tools Kit and requires it to be built.
Please note that RTTK does not and will not have a stable API, it is really meant as shared code between my other tools than a public library for people to use for their projects. You should use it only if you do not mind the occasional backwards incompatible breakage.