SocietalEclipse

http://spring1944.net/phpBB3/index.php USA, Britain, Russia, and Germany so far. Finland, Japan, and Italy are being worked on or planned for the future. The (subjective) downside is that the engine has spotty support for scripted singleplayer missions and there are no story driven progressive campaigns so the entire focus of the game is on multiplayer gameplay. The AI you can use for singleplayer is decent enough to enjoy a sandbox fight if multiplayer isn't your preference.

For me, "Other (Widescreen)" -> 2048x1152 (16:9) is my native resolution but I'm okay with using 1920x1080 in windowed mode.