RAPP Platform Wiki  v0.6.0
RAPP Platform is a collection of ROS nodes and back-end processes that aim to deliver ready-to-use generic services to robots
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(metapackage) RAPP-Platform-(metapackage)

The rapp_platform folder is essentially the RAPP Platform metapackage, where all the RAPP Platform dependencies are declared. As stated in the ROS webpage:

Metapackages are specialized Packages in ROS (and catkin). They do not install files (other than their package.xml manifest) and they do not contain any tests, code, files, or other items usually found in packages.

A metapackage is used in a similar fashion as virtual packages are used in the debian packaging world. A metapackage simply references one or more related packages which are loosely grouped together.