no they're not free afaik. zak is really old, it was first made available on the C64 and was really painful to play with digital joysticks (i did not have a 1351 (c64 mouse) at the time)
http://en.wikipedia.org/wiki/Zak_McKracken

oh and there's also "indiana jones: fate of atlantis" (not free either)

i'm listing these games because they're the best adventure games i've ever played. (oh and there's also simon the sorcerer 1/2)