GOG will remove Duke Nukem games from its catalog due to a court case earlier this year that selected a new rightholder for the five titles of the Duke Nukem franchise.
Among the titles involved are: Duke Nukem (1991); Duke Nukem 2 (1993); Duke Nukem 3D Atomic Edition (1996); Balls of Steel (1997); Duke Nukem: Manhattan Project (2002).
GOG hopes to bring Duke Nukem back; a post on the site says ‘we are in talks with the new rightholders to bring them back as swiftly as possible’.
As a 5-game bundle, GOG will offer a 90% discount. If users purchase the game individually, they will get a 70% discount.
3D Realms is no longer the owner of the franchise; Gearsbox has been selected as the new owner.
If you decide to buy these games, you got until December 31 at 10:59 GMT. After the mentioned time, “the games will be removed from sale soon thereafter, but they will not disappear from your shelf if you’re an owner.”
[Source]: GoG.com: Farewell for now, Duke Plus Last Chance to get Dragonsphere free.