[Louis Lessart]

What is NKP again?

It's Netkar Pro. It the pure-breed simulation Kunos Simulazioni made before Assetto Corsa. It started as a freeware (Netkar) and has been updated and released as Netkar Pro in 2006. The game was buggy in the first few years but after a few solid updates circa 2010 the game became quite enjoyable and a blast to play online. It's generally more difficult than AC with the cars being much more nervous but I find it more rewarding.

EDIT: to answer your question, the demo must have one track and one car in it if I remember well. The game was supposed to go freeware last year from what I heard but on their website they're not mentioning it being freeware, only support for existing licenses. The demo link doesn't seem to work, but there's a link on the right to download the full game. From what I read from last year, they are not checking the license anymore, maybe you can have access to the full game on the link to the right of their main page. My guess is that you might get the full game by now for free.