Civilization: Call to Power (1999)
Sid Meier's Alpha Centauri (continuing where Civilization II ended) (1999)
Call to Power II (2000)
Civilization: Beyond Earth (2014): Spiritual sequel to Sid Meier's Alpha Centauri.
There are of course other PC games that are related to the Civilization series but those are IMHO further away from the "main Civilization series".
SMAC was made by the same people (at least, some of the key people) that made Civ I-II, at a different company (Firaxis) from the one then producing and controlling the IP for the main Civ series (MicroProse) who had, IIRC, laid them off.
Several acquisitions and spinoffs of everyone involved, and all the rights are now with Take-Two, of which Firaxis is now a studio under the 2K games umbrella.
But I can't play those any more because I'm addicted to hex maps now. And pie menus. I hope Civ 6 has pie menus.