A quick search reveals that we've only written one post about venerable, free, turn-based strategy game Battle for Wesnoth. One! One. Burn down RPS right now. It's Fantasy Battles by way of Advance Wars, it's open source, it offers a vast selection of user-created campaigns and the latest update vastly improves the interface, the map editor, adds a new faction, and more. Let's increase that post count by 100% right now.
For a free and open source game, Wesnoth is frighteningly well-maintained. It's been fun to play for a decade, but it's been slowly becoming more professional in presentation ever since, to the point now where it's prettier (and better explained via its tutorial) than many paid-for counter-parts.
This new update improves the minimap, so it offers more useful information for players as they command their armies across hexagonal terrain. It also improves the add-on browser which is imperative, because while there are bundled official campaigns that come with the main game, most of your time is going to be spent playing on one of hundreds of user-created maps and campaigns, many of which have complete storylines to go with their battles.
The new faction is multiplayer only, but sounds interesting - a faction of humans which "lacks magic users, and instead specializes in using terrain features to coordinate attacks at dawn or dusk." High-accuracy melee fighters and horse-riding archers with high-mobility stats.
Of course, if you've never played Wesnoth before, none of this matters much. All that matters is that this game is great, free, and now a bit better. There are download links at the bottom of the v1.12 page.