GlorFindel: Dune, Dune II, Dune 2000, Emperor: Battle for Dune, Frank Herbert's Dune (video game).
I don't know the legal status of these games, but they sure are Unobtainable™!
There's a reason for this.
You will never see a re-release, remaster, update or other rejuvination of any of the Dune games because the current holder of the Dune estate (Brian Herbert), doesn't like video games.
And has when asked, said something along the lines of
"These games are old, and they should stay in the past." This is interesting, because Brian has okayed the re-printing of the books on several occaisions. And has seen fit to endorse a number of TV and film projects over the years, one of which is underway
right now.
Many of these things are several times older than any of the games.
But that doesn't matter, because Brian Herbert is a hypocrite.