[kiba]

Dwarf Fortress is about ten years old. Battle for Wesnoth is in development for 9 years. BZFlag is in development since 1992. Freeciv is in development since 1996.

The only game that in that particular list that is still in major continuous development is Dwarf Fortress. Everybody else is a completed game that is still improvement.

Duke doesn't really count, since their development is not really cumulative.

Commercial development tend to develop really intensely for several months to a short few years and make all their money in a few months. The're short term motivated and they will never develop their game beyond that. Yet, they took the equivalent of several decade of development time and never seems to goes beyond 40 hours gameplay.