Thanks!
Quick update - I tried the games so far.
Blockout (BLOCKOUT.GEO) was the closest to work.
The others complained about missing system files (which ?)
or were too large to fit on a single floppy (Blockgame, for example).
Could it be that the homebrew programs were written in R-Basic / NBasic ?
If so, I guess I have to find out how to copy the BASIC runtime to the floppy.
Edit: I also tried some utilities. The only two program thats worked were "Webmagik" and "Eurokonverter 2.0".
Well, their installers, installd.geo/webminst.geo, at least. Their icons were also shown correctly.
Also, when deleting the program files, it warned about them being "PC GEOS" files.
So now we do at least know that this thing is indeed running some form of PC GEOS! 😀
Edit: Pictures added.
Edit: Picture with the deletion warning added.
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In what to one race is no time at all, another race can rise and fall..." - The Minstrel
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