Interestingly, there's a free "Express" edition for download
Out of curiosity, went looking for more info as there wasn't any kind of reference/follow-up link in the article.
Main ClearPath info seems to be here:
There's also a free "ClearPath MCP Express" for download, which the description says:
"Students, teachers, hobbyists and ClearPath enthusiasts can use it for non-production evaluation, personal or educational purposes to explore and practice developing and testing ClearPath MCP-based applications."
Doesn't seem to be Open Source in any way though, which would have been nice. Oh well.