Source: https://freeciv.fandom.com/wiki/NEWS-3.1.0
Download: http://www.freeciv.org/download.html

WHAT'S CHANGED SINCE 3.0

The major changes in Freeciv 3.1 are new Qt6- and gtk4-clients, improved balance for civ2civ3 ruleset, experimental meson based build system, and a whole lot of extra flexibility to create custom rulesets.

As is usual for major releases, 3.1 clients cannot interoperate with pre-3.1 servers, and vice versa. Most pre-3.1 savegames can however be loaded into 3.1, and in most cases, the supplied rulesets have not changed so much as to make it difficult to complete a game started with 3.0.x's rules.