Quote from the website:

“Zak McKracken: Between Time and Space” is an unofficial sequel of the adventure-classic “Zak McKracken and the Alien Mindbenders” which was released in 1988. We (a bunch of adventure-fans) made it our task to use the theme of this impressive cult-game and create a sequel which follows in the footsteps of the classic adventure games, but at the same time delivers a brand new experience. (end of quote)

This game can be downloaded for free, it is about 2 GB large. I am not sure if it is available in English yet - the English website reads:

“The game is not yet released :P”

• Original website:
  www.zak2.org

Remember:
This is a fan project and no official sequel to “Zak McKracken And The Alien Mindbenders” by LucasArts!