Zombie Smashers X is a 2D

2D computer graphics

2D computer graphics is the computer-based generation of digital images—mostly from two-dimensional models and by techniques specific to them...

 sidescrolling fighting game

Fighting game

Fighting game is a video game genre where the player controls an on-screen character and engages in close combat with an opponent. These characters tend to be of equal power and fight matches consisting of several rounds, which take place in an arena. Players must master techniques such as...

 for Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 from Ska Software. It was released in 2001

2001 in video gaming

-Events:* Academy of Interactive Arts & Sciences hosts the 4th Annual Interactive Achievement Awards; inducts John Carmack of id Software to the AIAS Hall of Fame...

 as shareware

Shareware

The term shareware is a proprietary software that is provided to users without payment on a trial basis and is often limited by any combination of functionality, availability, or convenience. Shareware is often offered as a download from an Internet website or as a compact disc included with a...

 and then re-released in 2006

2006 in video gaming

-Events:* January 26, 2006 -- Nintendo announces its newly redesigned handheld, the Nintendo DS Lite. The new model is lighter, smaller, has configurable brightness and features an improved user interface.* January 26, 2006 -- Konami Corp...

 as freeware

Freeware

Freeware is computer software that is available for use at no cost or for an optional fee, but usually with one or more restricted usage rights. Freeware is in contrast to commercial software, which is typically sold for profit, but might be distributed for a business or commercial purpose in the...

. Zombie Smashers has yielded two sequels with a third on the way.

The old website's introduction of ZSX:

Zombie Smashers X has a gripping, fantastic plot in which one or two characters realize(s) that Earth is becoming overrun by zombies and decide(s) to do something about it.

The fighting system is basically a tribute to River City Ransom for Nintendo: street brawling with an RPG twist. Each player has stats which can be upped by buying and eating food; special moves are learned by purchasing tattoos. As the game progresses the monsters and bosses become increasingly powerful so its important to power up. The scenery is pretty diverse and interesting and encompasses one big constant world to explore.

Gameplay

ZSX is a pure button-mashing game. You spend the most part of the game pushing the punch, kick and jump button.
The twist is, the blood effects, the fitting sounds and music whip you, and with the crunching effects the many (sometimes even improvised) weapons, you can be held busy for hours with a very simple gameplay the average gamer adores.

Story

Earth has become overrun with zombie

Zombie

Zombie is a term used to denote an animated corpse brought back to life by mystical means such as witchcraft. The term is often figuratively applied to describe a hypnotized person bereft of consciousness and self-awareness, yet ambulant and able to respond to surrounding stimuli...

s and the player must fight to free the world and send the zombies back to the grave.
During the trip, he encounters bosses that, during the pre-fight conversations, explain and unfold the story pace by pace,
telling that eventually The One is the cause of all this.

The One

Even though the player does not know at first, the One, a devil that can be held as (but is not be referred to as) Satan, is the cause of the zombie-plague coverring.
He gets defeated in a battle that truly is tougher than most bosses you encounter.