By that I mean the option to just pack up and move your assets to other locations, not being bound to where you started. It has to just be an option, not the primary playstyle as there are plenty of games with no base-building. Examples I know of include:

- Imperator: Rome, migratory tribes can move the entire population out of a territory as long as it's 20 pops or less, and resettle it elsewhere as tribesmen. Even occupied hostile territory.

- Endless Space, iirc one or two of the factions can relocate everything out of a planet, including buildings.

- Thea 2, you never have to actually use your Seed to construct a village and in fact it has other uses.

- Europa Universalis 4, north American tribes can migrate regularly until they gain a second province.

As far as I remember Command and Conquer 4 has the ability to move your main building.

The Night Elves in WC3 can "uproot" most of their base buildings, the Eldar in Dawn of War can also teleport buildings too via webway as I remember.

Starcraft: Humankind can relocate most of their buildings. Maybe you want to mean Endless Legend. Don't remember the name now, but it was the nomads who are masters of commerce and whose quests revolve around dust.

Nah, I was thinking of the Pilgrims in Endless Space, which have pretty much exactly the kind of thing I'm looking for:

''The Pilgrims affinity allows them to evacuate an entire system. After 3 turns, the system will be emptied of all its structures and population except for planetary exploitations and one pop per planet. A special colony ship will be created carrying them. Upon settlement, the new planet will have all the removed structures and population; if there are more population than capacity, additional planets will be automatically colonized for free within the same system. If there is still insufficient room, the excess population is lost. The Crowded Planets perk seems to be ignored at this step, meaning you can both settle additional planets or lose population by going beyond the uncrowded limits. Unlike producing a normal colony ship, the evacuation does not prevent planetary growth while it is under construction.''

Total War: Attila

Total War: Atillia has nomadic factions which begin the game without a city. The only way to survive is through pillaging.

Crusader Kings 2 - you can play nomadic in that (the mongols for instance).

Interesting. Another game for you: in Civilization: Beyond Earth there is a a naval faction that can relocate their sea cities.

Nomadic gameplay is interesting as opposed to one based on a more intensive use of the land. More difficult to figure out by game designers, unless they study how proper real nomadic cultures function.

There is an official scenario in Civilization IV (Warlords expansion) that lets you play as a nomad Barbarian horde. Your goal is to annihilate all traces of civilization. :D

In civ 1 or 3 you can move your capital to another city and then abandon the first.

or in one of those you can even make a settles which turns the entire city into that settler, if you time it right

Homeworld?

I think Oriental Empires had that sort of feature introduced in DLC, but since I don't have DLCs for that game, I can't say first-hand.

There was a trait you could pick while creating your potential empire in Stars! that made it so you didn't actually settle planets, but lived around them.

The Zhon faction in Total Annihilation: Kingdoms was designed to be nomadic, with mobile units having the ability to produce other units, and only a scant few stationary buildings.