free & opensource version: http://www.freeciv.org/ web version: https://play.freeciv.org/
Man, that AI. In Civ 1, on the lower difficulties I could happily defend myself and expand my borders and explore the world. FreeCiv doesn't exactly have a "difficulty" setting—it's got like twelve pages of buttons and sliders—but on the default difficulty it seemed like I always spawned next to two or three other civs that would near-immediately grind me to paste.
I really, really wanted to like FreeCiv, but I don't think it likes me.