Where is the line between what is and what is not a video game? As fascinating as all the complex, cinematic games of the past few years can be, some of the most engrossing games out there are the ones that are so simple they barely qualify as games. Of any gaming company in the history of the industry, none have been better than Maxis at releasing titles that can easily occupy four hours of play-time before the player knows it. What's more, they've managed to do this with extremely simple games.

Back in 1994, Maxis published a game developed by OPeNBooK, a company established one year earlier by Yutaka Saito, the same man behind the development studio Vivarium (which would later merge with a more modern iteration of OPeNBooK). That game was Sim Tower: The Vertical Empire. The inherent simplicity and limits of the game led Maxis to brand it as a "software toy" rather than a "game" outright.

Maxis was already famous in the computer gaming world for their Sim City series. The wildly popular Sim City 2000 came out just shortly before Sim Tower hit the shelves. The premise is simple, at least on the surface. Players are presented with a blank lot where they can build their tower one floor at a time. The player view looks into the building from the side as if one of the walls is missing. Blank spaces on each floor can be filled with different kinds of functional space, like offices, stores, hotel rooms and condominiums. As the population and height of the tower increases, so do the building options.

The real challenge of Sim Tower isn't resource management (it's actually pretty easy to rake in a lot of Simoleons), but it's definitely tough to use your limited space wisely. Getting your tower-dwelling Sims from place to place is no small task, especially when the tower grows tall enough to have additional lobbies (every 15 floors). The game only allows players to create so many elevator cars, so it's not just a matter of waiting until there's enough money to max everything out.

The beauty of Sim Tower is how it rewards being observant and planning ahead. It's no small task to achieve the "Tower" rating, which is the highest possible achievement in the game. Like all of the Sim games, there is no real "end" to Sim Tower, only a point beyond which nothing else can be done. But the journey to that point is a heck of a lot more entertaining than a real estate management simulator ought to be.

Sim Tower saw some limited console ports, including some generic clones and portable versions. Saito eventually developed a sequel, Yoot Tower, though it didn't see widespread success or distribution. As a sequel, most of the additions are cosmetic or add to micromanagement. The concept behind Sim Tower is solid enough that could make for a very interesting game on a modern computer or console. It would certainly be thrilling to construct a fully 3D tower, then be able to walk around it with an avatar in real-time. As yet, no developer has really approached the idea of a complex building simulator.