(Disclosure: This site contains product affiliate links. We may receive a commission if you make a purchase after clicking on one of these links. Read our affiliate disclosure for more info.)
There’s supposed to be a multiplayer demo of Arma II released later this month. It’s called Arma II: Free (A2F). You can play online with regular users. You won’t get the full campaign and it’s limited to low resolutions but you can try the game out before purchasing at least.
The free version of the game does not include the campaign mode, HD graphics or support for user-made addons and mods. It does, however, include the full range of over 300 weapons, units and vehicles; the 50+ player multiplayer mode; support for play on dedicated servers from either the free or retail version; and the single/multiplayer mission editor. There are no microtransactions and no hidden costs in the game — it’s completely free, effectively making it the world’s most generous demo.