RHAPS - Redhat Applications Server: for building content management systems, intranets, portals, and custom applications
RHCS - Redhat Cluster Suite: designed specifically for Red Hat Enterprise Linux systems. Companies requiring applications to be highly available, or wishing to improve the performance and availability of their network infrastructure, should consider using a Red Hat Cluster Suite configuration.
RHDS - could be Redhat Differentiated Services: a protocol for specifying and controlling network traffic by class so that certain types of traffic get precedence - for example, voice traffic, which requires a relatively uninterrupted flow of data, might get precedence over other kinds of traffic.
RHGFS - Redhat GFS is a cluster file system that provides data sharing among systems. Red Hat GFS features a single, consistent view of the file system name space across all nodes in a cluster. It is a native file system that interfaces directly with the VFS layer of the Linux kernel filesystem interface.
Hope that helps.