PlayCast (among many others listed at the bottom of the article) and now yet another alternative called PS4Play is here!
The free PS4Play software to play PS4 and PS3 games on PC with keyboard / mouse can be found on their official site www.PS4Play.com along with a preparation guide, and below are some PS4Play demonstration videos:
PS4 Control by Keyboard and Mouse
PS4Play Mouse Config CN/EN
Cheers to @Abkarino for the news tip!