[HTML1]

Most free-to-play online games are social apps (i.e. Facebook), MMOs (i.e. Neverwinter, Star Trek Online) or competitive multiplayer titles (MechWarrior Online, Tribes: Ascend), but not many take the form of a full-on co-op game. That's just one of the many things that makes Warframe special.

Warframe is a third-person action game by developer Digital Extremes, that mixes shooter and melee combat, with fantastical powers, RPG elements and even looting. The game hit in open beta last week and after loving the closed beta, we tried out the latest version with Update 7 to share some gameplay footage.

The open beta date for Warframe could not have come at a greater time, on the heels of the announcement that Mass Effect 3 will not be getting any additional multiplayer content. Why does that matter? The simplest way to describe what Warframe is to say it's what Mass Effect co-op multiplayer should have been. It offers the gameplay elements of combat and environmental traversal better, and it looks gorgeous throughout.

Warframe lets players form a party of up to 4 players (it can be played solo as well) and travel the stars, from planet to planet, completing missions and earning credits, experience and materials. The game's title is the name of the armor the players wear and it - like all of the game's weapons - can be leveled up and upgraded with mods collected or purchased. Even the mods themselves can be scaled up.

They were called Tenno. Warriors of blade and gun: masters of the Warframe armor. Those that survived the old war were left drifting among the ruins. Now they are needed once more.

The Grineer, with their vast armies, are spreading throughout the solar system. A call echoes across the stars summoning the Tenno to an ancient place. They summon you.

Allow the Lotus to guide you. She has rescued you from your cryostasis chamber and given you a chance to survive. The Grineer will find you; you must be prepared. The Lotus will teach you the ways of the Warframes and the secrets to unlocking their powers.

Come Tenno, you must join the war.

There are three enemy factions players encounter, and they scale up, add new units (including bosses) as players progress. The game features over a dozen unique Warframe suits, each coming with different attributes, and most importantly, with entirely different sets of powers. Players equip their Warframe with a melee weapon, a primary gun and a sidearm, much a wide array of different types. Weapons can be unlocked with experience, in-game credits, real-money transactions (Platinum) or built with blueprints and acquired materials.

All of the purchasable goods can be acquired by playing the game so players are never locked behind pay walls. We'll let the game speak for itself, so watch and enjoy our preview video up top. It begins with a 2 minute discussion of the game and then jumps into three different missions that highlight different maps styles, different mission and enemy types, and even three different Warframes in action playing cooperatively. For a legitimate look at how gorgeous Warframe truly is however, we recommend you watch the video in 720p.

Warframe is a ton of fun, easy to get into, and above all it's free. Did we mention the four-player co-op part?

Interested in trying Warframe - download the game for free at warframe.com.

Warframe is currently in open beta for PC.

Follow Rob on Twitter @rob_keyes.