By Brad Cook

You stand on a sun-splashed Guadalcanal beach, watching a Japanese Zero dogfight with an American P-51 Mustang. Off the coast, an American battleship pounds a Japanese position with its massive guns. A pair of tanks rumble past, making a beeline for some enemy armor in the distance. And then you see them, marching over the crest of a nearby hill — three pirates, their muskets at the ready.

You level your musket and fire, the powerful blast knocking one of them on his back. The others advance, returning the attack. A bullet slightly injures you, but you manage to dance around their shots while reloading. Again you aim, but the odds are too great: their barrage overwhelms you. Time to respawn, but the loss of your team’s positions on the island means you must reappear on a pirate ship out at sea.

No, something funny didn’t happen to your Mac. We’re simply describing the same battle as it would look while playing a regular Battlefield 1942 match, and then as it would look after activating the Pirates modification for the game, turning your World War II battle into a contest between scurvy dogs. Also known as a “mod,” Pirates is one of many free downloads that morph your favorite games — Battlefield 1942, Unreal Tournament 2004, and Civilization IV, among others — into entirely new experiences.

Defining Our Terms

For the purposes of this article, we’re talking about mods that partially or fully replace the content that originally came with their host games. For example, the Red Orchestra mod for Unreal Tournament 2004 turns that science-fiction-themed first-person shooter (FPS) into a World War II-themed FPS, so you’ll see it covered here. However, add-ons for The Sims 3, among other games, won’t be addressed because they augment the existing content, rather than replace it.

We also aren’t talking about games, such as SketchFighter 4000 Alpha and Warcraft III, that include tools for making your own maps set in those worlds. While we agree that they’re a lot of fun to play with, they also fall under the heading of content extension, rather than content replacement.

Before you download and install any mod, make sure you have the latest version of the game in question, and double-check that it will work with the game’s expansion pack, if you have it. Visit the publisher’s support site to download any patches, or search for the game at MacGameFiles. When looking at mods not covered in this article, be sure to check their system requirements, since some of them are Windows-only. (Even if you’re told a particular mod only works with the Windows version of the game, do a quick Google search to see if someone has created a Mac-compatible edition. Many mod developers are happy to fulfill such needs.)

We’ve highlighted the best mods we’ve found, but many more exist. Read the listings at MacGameFiles.com to find additional downloads. Visit Apex Mods to learn more about Heroes Unleashed for Tom Clancy’s Ghost Recon, which packs more than 100 single- and multi-player maps and missions into one bundle. Finally, the Wikipedia article that covers computer game mods also delves into the many that exist for older titles, such as Deus Ex.

Action Game Mods

Action game mods tend to be the most popular, probably because many of the earliest mods were based on the best-selling first-person shooters Doom, Quake, and Unreal. (See our sidebar, “A Brief History of Mods,” for more information.) You can download plenty of mods for the latest versions of all three, along with mods for Battlefield 1942 and even a mod for the venerable Freespace 2 that turns the game into Battlestar Galactica: Beyond the Red Line.

Last Man Standing (LMS) is a Doom 3 mod “that aims to bring back the classic Doom experience,” according to the team that created it. It features wave after wave of attacking monsters, challenging you to be the last marine standing when the carnage ends. You can progress through different levels in the game, rather than play in the same map over and over, or take the action to a defense map, where you and your fellow marines must protect a certain area or person, or accomplish other goals.

Of the many Unreal Tournament 2004 mods available, which include one featuring Robin Hood, Red Orchestra is one of the most notable, turning the science-fiction first-person shooter into a World War II battle between the Soviets and the Germans. Eschewing the health packs and oodles of ammo found in a typical Unreal Tournament 2004 match, Red Orchestra puts the emphasis on realism: a shot in the leg will seriously slow you down, while one in the head means instant death. Teamwork is key to survival.

Many mods also exist for Battlefield 1942, including the aforementioned Battlefield Pirates and Battlefield 1918, which takes place during World War I. If you’d rather fight during the present day, take a look at Desert Combat, a mod focused on Middle Eastern conflicts that have taken place over the past decade.

And if you’re really in the mood for some nostalgia, Team Unpfhorigven has recreated Bungie’s classic game Marathon as an Unreal Tournament mod known as Marathon: Resurrection. It features 27 solo and 16 multi-player maps, new weapon and monsters, and more. While the mod aims to recreate the original Marathon experience, it also throws in some fresh changes designed to give the fans a reason to play through the game again.

Strategy Game Mods

The strategy genre is also home to many mods, beginning with Civilization IV, which was designed with modifications in mind, thanks to its use of the XML file format for game attributes. XML files can be easily changed, allowing players to add new content to Civilization IV with few complications. A handy all-in-one installer is available, simplifying the process of downloading and installing mods.

Differences in the ways Windows and Mac OS X handle XML files has led to some Civilization IV mods not working well on the Macintosh, but a thread on the Civilization Fanatics forum notes which ones should be error-free. Civilization Fanatics is a great resource for not only mods but also all kinds of information about the popular strategy series.

The Ancient Mediterranean mod for Civilization IV features 20 new civilizations, including the Phoenicians (ruled by Hiram), Bablyon (Hammurabi), and Carthage (Dido). Those civilizations progress along a new ancient technology tree, with their corresponding military units and heroes. New maps and reworked AI round out the experience.

If you’d rather explore more recent history, the Age of Discovery mod, set in 1492, allows you to play the European point-of-view (England, France, Spain, or others) or the Americas point-of-view (Native Americans, or the Aztec or Mayan Empires). In addition to featuring the relevant technology, this mod also introduces traders, who ply the seas taking their wares between nations, and pirates, who can capture traders and bring wealth to those who sponsor them.

And don’t forget that the Civilization IV expansion pack Beyond the Sword comes with 11 mods, including Afterworld, a squad-based futuristic scenario that pits you against hordes of zombies and the undead and Civ Defense, which challenges you to withstand waves of enemies determined to destroy your cities; earn gold to fortify your position before the next group arrives.

Or take a shot at the granddaddy of all Civilization IV mods: Rhye’s and Fall of Civilization, which places all of the game’s empires into their proper historical context as time passes. Each ascends and declines the way it really did, with a stability rating that dictates its security and a unique historical victory condition, such as defending the American continent as the Aztec Empire.

More Strategy Game Mods

Command & Conquer Generals and its Zero Hour expansion pack also offer a wide variety of mods. One of the most impressive is Blitzkrieg 2: The Finest Hour, which turns the game into a World War II recreation in which you take control of the Allies, Germany, or the Soviet Union, complete with authentic buildings and units.

Or leap ahead four decades to the height of the Cold War in the Cold War Crisis mod. The USSR and the United States face off between the years 1980 and 1989 in a total conversion that features high-quality graphics, a custom soundtrack, and even professional voice-overs. Play online or single-player against a robust computer-controlled opponent.

For more strategy modding fun, try out Fleet Commander, which takes the futuristic universe of Homeworld 2 and flings it into the distant past, where humans and Cylons struggle against each other while searching for a mythical planet known as Earth. Or peruse the mods available for the nuclear annihilation game DEFCON, including one that evokes the movie WarGames and another that takes you to Middle-Earth. Finally, Heroes of Might and Magic V offers a very robust modding community.

Role-Playing Mods

The last major genre for game mods is one of the oldest in the world of computer gaming. From the earliest days, players yearned to recreate Dungeons & Dragons and other pen-and-paper role-playing games on their computers. Today, Neverwinter Nights 2 faithfully translates D&D on your Mac, complete with authentic rules and the ability to take on the role of Dungeon Master and guide your friends through a game. You can also find plenty of modules to download and play, some of them wholly original and others based on classic paper D&D modules, or based on such well-known worlds as Middle-Earth.

And if you’d really like to immerse yourself in some nostalgia, download the Ultima V: Lazarus mod for Dungeon Siege and relive Richard Garriott’s popular 1988 game Ultima V: Warriors of Destiny with current technology. The story involves a tyrant who has taken over Britannia and is enforcing a strict moral code with help from his three brutal Shadowlords. Only you can restore Lord British to his rightful place on the throne.

Finally, we’d be remiss if we didn’t mention the mods available for World of Warcraft. While they don’t fit the definition we laid out at the beginning of this article, they’re still worthwhile tools that give you useful information about other characters and monsters, provide additional maps to browse while playing, and more. World of Warcraft clearly represents the future of role-playing.