I think windows is the main thing holding crystal back. I make little games for jams and I'm always trying out new languages. I submitted a bug related to running processes on windows last november, it was just recently closed as completed. Although I spend almost all of my at-home time on linux, I know that I have to provided windows executables for jams. I plan to come back to crystal when I can write once and can compile the same code everywhere.
I started to use Crystal in a small commercial project, as a web backend, and it was very fun and promising.
But the project got cancelled for completely unrelated reasons.
I long for an excuse to use Crystal again. Hard typing combined with Ruby carefree style and EXEs without runtime... really cool stuff.
I think Crystal will crack the Win32 nut eventually.