Official, unmodified ADFs are technically still under copyright, though they are often bundled in commercial packages like Amiga Forever The Verdict:
This is the core bootable operating system disk. It includes the graphical interface and essential system files.
When you boot a Workbench 1.3 ADF file, you encounter a highly structured environment packed with essential system tools.
It improved the ability to boot from hard expansions, which was a game-changer for the "Prosumer" market.
Alex's heart skipped a beat as he carefully retrieved the diskette. He remembered the countless hours he spent playing games, creating graphics, and experimenting with demos on his Amiga. The Workbench 1.3 ADF (Amiga Disk Format) diskette was a special one – it contained the installation files for the Amiga Workbench 1.3 operating system.
If you are diving into Amiga emulation, the Workbench 1.3 ADF is your primary boot disk. While many Amiga games are "trackloaders" (meaning they boot directly into the game without needing an OS), the Workbench is required for:
Do you need help finding legal Kickstart ROMs?
, font editors, and various system tools that expanded the OS beyond the standard desktop. Usage via ADF (Amiga Disk File)