Explaining XADMASTER and XFDMASTER

XADMaster and XFDMaster are helper libraries used on Amiga-like systems, including AROS distributions, to make archive handling and decrunching easier for applications. XADMaster XADMaster is a library system for unpacking archives.
It is used when a program wants to read or extract compressed archive formats without implementing every unpacker itself. 

Typical archive examples include formats such as:
.lha
.lzx
.zip
.tar
.gz

other Amiga or cross-platform archive formats, depending on installed clients

The basic idea is: 

Application↓
xadmaster.library↓
XAD client for the archive format↓
Archive contents are listed or extracted 

So instead of every file manager, installer, or unpacking tool needing its own LHA, ZIP, or TAR code, it can ask XADMaster to handle the archive. 

Where it is used 

XADMaster may be used by: archive extraction tools
file managers
installers
package tools
utilities that need to inspect or unpack archives
programs that support compressed file browsing

Simple beginner explanation 
A beginner can think of XADMaster as: a central unpacking system for archives. I
f the right XAD client is installed, programs can use XADMaster to understand that archive format. 

XFDMaster 

XFDMaster is a library system for decrunching compressed executable or data formats, especially older Amiga-style cruncher formats. On classic Amiga systems, many programs, demos, tools, and game files were compressed with so-called crunchers. These were not always normal archives like LHA or ZIP. Often they were packed executables or data files.

The basic idea is: Packed/crunched file↓
xfdmaster.library
↓XFD decruncher client↓
Original unpacked data 

Where it is used XFDMaster may be used by: 
decrunching tools
virus checkers
file identification tools
retro utilities
demo/game preservation tools
programs that need to inspect packed executables

Simple beginner explanation 

A beginner can think of XFDMaster as: a central decrunching system for old Amiga packed files. It is especially useful for old software collections where files may be compressed with historic Amiga crunchers rather than normal archive formats. 

XFDMaster is mainly for decrunching old packed files. 

In simple terms: XADMaster = archives
XFDMaster = crunched executables/data 

Both provide shared unpacking/decrunching services so that AROS applications do not need to support every old Amiga format directly.   WHDLoad is mainly a classic Amiga system for installing and running floppy-disk-based Amiga games and demos from hard disk. In the AROS context, it is best understood as a compatibility-related tool, not as a normal native AROS application system.