Is there anything to recommend?
It was a long time ago I played these so I don't remember anything that stands out. I remember that frisbee game (you are a dog that tries to catch a frisbee thrown at you over and over), a racing game (like HuZero but more simple), a very hard game where you bounce on disappearing platforms (very primitive graphics), some sound test-like programs and the mentioned mouse rakugaki program (I recently tried this one with my mouse).
There's nothing really great, just fun to see that people actually made their own creations for the system.
The number of homebrew games aren't great, but there are also lots of other things like artwork and songs made with those public tools on these CDs. I think Develo Magazine also had demos of commercial PC Engine games like Fray on the CD as well. And the Develo Starterkit CDs of course has the Develo software on the CD for communicating with the Develo Box peripheral and a PC.