Nuclear Dawn
Developer: Nuclear Dawn Development Team
Website: www.nuclear-dawn.net
Price: Free conversion for Half-Life 2.

From the website:
Nuclear Dawn is a FPS/RTS multiplayer only Modification for Valve's Source Engine.

On The Field:

• Three distinct classes to choose from with strengths and weaknesses that will help you overpower your opponents or keep you on guard.
• A wide arsenal of weapons to deploy on the battlefield including mines, grenades, rifles, rocket launcher, and much more.
• Original environments rich with detail and perfect for a nice and bloody battle. Take the streets of a desolate Japanese city, venture into the jungle to capture the live warhead inside a Korean nuclear silo, or fight for the treasures of one of several other post-apocalyptic locales.

As a Commander:

• Objective-based game play emphasizes coordinated tactics.
• The environment and physics shape your strategy. Create chokepoints, defensive positions, and blast your way through the enemy positions.
• Build a multitude of different structures to aid your team in its conquest. From a gateway that can bring in reinforcements directly to the battlefield to turrets that will pound your enemies into submission.
• Choose your team's path with an intuitive but deep technology tree.
• Secure resource points to deploy weapons and equipment to aid your team.