Civ V: Idea for a new unit (mining colony)
I remember in Civ IV you could break cities off to form colonies, which would function independent of your civ, but you would get the benefit of its science and resources without the penalties of another city to maintain. Although I think to form a colony in IV the city/cities had to be on a separate continent. I remember in a Civ IV game I didn't have a resource I needed, but there was some on a small unclaimed island. I sent over a settler, made a city, and turned it into a colony so I could get the resource without the extra hassle of another city to maintain.
I'm in a similar situation in my current Civ V G&K game. I just researched iron working which reveals iron on the map. As my luck goes, there is no iron in my borders. There is one source two blocks outside the border of my capitol, but it's too far out to buy the tiles and I don't think the borders will expand any farther. I want that iron, but it's in a bad location and not worth putting a city there just to get it.
I had an idea for a unit like a settler, but instead of making a city it would put up a mining colony so that you can get resources from outside your borders in unclaimed territory without having to build a new city. It wouldn't have territory borders, but it would have a range around the colony that would let you mine/farm the resources in its range. The farther from your border, the more expensive it would be to build and/or maintain. It also can't defend itself, so you would need to guard it from barbarians and other civs.
I wonder if this could be modded in, but it would be nice to have in an official patch or something to put in with the next expansion.
Personally I have always liked this idea.
There is plenty of precedent for this idea in Civ and related games. I believe it was CivIII that had the colony concept where you could sacrifice a worker to build a colony on a remote location in order to harvest the resource, of course in CivIII you also had to build a road to the colony. I also think SMAC had a similar concept with crawlers that could be moved to a resource to harvest it.