ETH Oberon V4 for Atari ST & TT computers.
Extract the zip, and in the zip further extraxct the SYSTEM.LZH with 7zip. Put the content of SYSTEM.LZH on your harddisk. Then run KERNEL.PRG to start Oberon. The other two Arc files are the sources and fonts compressed with the Oberon Compress tool in Oberon. You can run ST-Oberon also on a PC with an Atari emlator like STeem.