The free-to-play game Freeciv has an unlimited number of modes and possible mods, but its default mode (at least the one downloadable in mid-2011) has a great deal in common with Civilization II. There are some small differences and some major differences. Players familiar with Civ2 who switch to Freeciv can simply read the Help and other in-game menus and the relevant pages on the Freeciv wiki, but some details deserve particular note if you want to take full advantage and/or avoid nasty surprises.
This is a welcome addition, available with Pottery. Cheaper (at 30) than Settlers or Engineers and not reducing its host's population, it does not have the ability to build cities, but can do everything else that Settlers can do. Obsoleted by Engineers,(because they are cheaper)so build lots of them just before you discover Explosives if you have Leonardo's Workshop.
They make Workers obsolete and do not make Settlers obsolete: they are essentially double-speed Workers, with the additional transformation power as for Civ2.
Their Attack strength is now 3, not 2. This makes more sense in the progression from Phalanx (1/2/1) to Riflemen(5/4/1).
Library and University
More value for the same maintenance cost. Library adds 100% to your basic science, and University adds another 150%.
Marketplace and Bank
Maintenance cost of 0 and 2, respectively. In a way, that makes up for their adding only the 50% each that they do in Civ2, which keeps them fairly competitive with the science buildings, at least in the early days.
Much more use than in Civ1, and never expiring, but not as good as in Civ2: adds HALF a Granary to every one of your cities. If you have no granary, your food box is 25% full after population growth. But Pyramids is cumulative with the granary, so if you have a granary your food box is 75% full after growth.
It has the same result, for the most part; some grasslands become desert and some land tiles next to ocean turn to swamp. However, there is, apparently, no warnings about imminent catastrophe. There is also the misleading indication in the popup you get by hovering over the indicator: after the first unexpected catastrophe in a recent game using v 2.2.5, with little or no reduction in pollution since the previous turn, that message said:
Shows the progress of global warming: Pollution rate: -5% Chance of catastrophic warming each turn: 0%
Presumably the "-5%" is an indication of the cleanup going on, subtracted from the new pollution being generated.