Targetware is both Mac and PC also Linux too. Right now we've got 4 major modules under development that can be played online; Target Rabaul (PT

, Target Tobruk (MT

, Target Korea, and Richthofen's Skies. These mods are volunteer based. Both the mods and the game engine are being developed and are by no means finished. It's main focus is online, realistic FMs and game play. The game realism in game play suffers a bit now because full plane sets and game engine functions aren't ready yet, same with the FMs to some extent.
Right now it's free for DL and online play. There are never huge numbers of people online but you can usually find a few people to shoot at

It's frustrating for people new to flight sims and has a steep leaning curve at first. Fly around for a bit and you'll pick it up fine.
Give it a try
http://web.targetrabaul.com/modules....download&cid=6