As I know, FreeType restrict some features by patented font technology from Apple. So, if I develop a program for Apple platform only, can I enable and use the features?
This would not be allowed "by default," only if Apple somewhere licenses their patents to you. I'm sure they license them for their APIs but FreeType seems doubtful.
However, haven't the patents expired anyway? see http://stackoverflow.com/questions/3726801/freetype-patent-issue