I host current sources for Oberon V4:

Only the Sparc and the Linux version are actively maintained. The other sources have not been modified for several years. If you have more up to date versions of any source, please submit them to v4@claudio.ch so that I can upgrade the source archive.

This table gives an overview about all modules contained in this archive. You can see which modules are the same and which differ between V4 implementations. This is a good base to see where a module might be replaced, so that the difference between V4 implementations will be reduced. If you find that in one implementation a module can be replaced by one of an other implementation, please notify me.

You can find Oberon V4 for some other systems, though without sources, on the FTP server of ETH Zurich and University of Linz.