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Liero is a video game for MS-DOS, first released by Finnish programmer Joosa Riekkinen in 1998. The game has been described as a real-time version of Worms (a turn-based Artillery game). It has many weapons and sounds from its precursor, MoleZ. 'Liero' is Finnish for earthworm and is pronounced [liero]. Later on, this game provided inspiration for the game Soldat.
In Liero, two worms fight each other to death for score (or frags) using a choice of five weapons from a total of 40 in a two-dimensional map. Most of the terrain, except for indestructible rocks, may be dug or destroyed by explosions. In addition to the weaponry, each player has a ninja rope which can be used to move faster through the map. This grappling hook-like device substitutes for jetpacks and can even latch onto the enemy worm to drag him closer to his foe.
While playing, there are health power-ups to heal your worm. It is also possible to replace one of your five weapons by picking up bonuses. Before playing, you can select certain weapons to be available only in bonuses, in the entire game, or completely disabled.
Unlike most side-scrolling deathmatch games, the weapons in Liero have infinite ammo. Key factors include the reload rate of each weapon and how fast they shoot, whereas in most others include how much ammo a gun sports and how frequent more ammo for that gun can be found. Liero depends all on timing and swift maneuverability.
The gameplay mode can be deathmatch, Game of Tag or Capture the Flag. It can be played by two human players simultaneously in split screen or in a single player mode against the game's artificial intelligence, although the game's popularity is derived mostly from the fast-paced player-vs.-player action it provides.
Liero's last release was version 1.33, released in 1999. However, the author lost the Pascal source code in a hard disk crash, and due to the lack of backup, no new "classic" versions have been released since. Despite this, and with the author's approval, the Liero community has distributed several altered (or hacked) versions of the game through the LieroCDC, and others. In 2009, "classic" Liero was officially merged with the OpenLiero project upon the release of Liero 1.34 (not to be confused with the total conversion by that name). The new versions are released by Gliptic, although Joosa Riekkinen endorses them as official.
Liero is a versatile game in terms of modification. All of its 40 weapons can be completely replaced with new ones that can be given different images and sound effects from the original set. The images of the worms themselves can be transformed into completely different characters, although their movement animations are less flexible regarding modification. The maps can be given permanent terrain other than rocks alone. Destroyable terrain can also be colored more than simply plain dirt. The AI can be modified to be harder or easier. Nearly the whole game can be converted into something entirely different, except for the main aspect having to do with slaughtering another player/AI.
Clones and remakes 
Liero Xtreme 
Liero Xtreme (often called LieroX, Liero Extreme or just LX) is a 2D shooter game. It is an unofficial sequel to Liero, and is the most popular of all the Liero clones. It features online play, fully customizable weapons, levels and characters. Liero Xtreme was created in C++ by Jason 'JasonB' Boettcher, an Australian programmer. With its source release on April 10, 2006, a new project has become available on October 24, 2006, known as OpenLieroX, while the development of the original LieroX project has stopped. At the time of writing (May 6, 2009), OpenLieroX has tripled in code size and has many new features.
The game is based on a deathmatch setting, where multiple players face off in a closed level. Each player is equipped with five weapons selected out of all the weapons allowed, and with a ninja rope that allows the player to move in any direction. Players begin with a set amount of lives, and whilst the game records the number of kills, the last man standing is usually considered the winner. Liero Xtreme also allows team deathmatches, which has made it common for players to form clans. OpenLieroX runs on Windows, on MacOSX, on Linux and on FreeBSD.
The first release announcement of Liero Extreme was made on October 14, 2002. LieroX has become very famous over the time. On February 14, 2006, Jason Boettcher stopped the LieroX development for good. The last version he released was 0.62b, which had many new features, but suffered from crashes and various errors, and did not catch on within the community which continues to play the 0.56b version. Before leaving the community, he released the source code of the even older version 0.55b under the zlib license. Development of LieroXtreme is now in hands of Karel Petranek and Albert Zeyer, used the source code to create OpenLieroX, which is compatible with the popular 0.56b version, but has multiple new features and bugfixes. Michał Futer took care of the new frontend. Currently the majority of players play OpenLieroX.
As a customizable game, it allows players and developers to script their own mods. Different mods have different sets of unique weapons, and may also differ in player gravity and movement. The default mod is Liero 1.0, also called Classic, which is roughly equal to the basic setting in original Liero. On top of this, several player-created mods are included in the standard game packs, some of which are more popular than the default setting. Similarly to Liero, the default level is Dirt Level, consisting of diggable terrain with some indestructible rock. The default level is comparatively rarely played compared to more complex player-created levels.
The game interface allow players to modify factors of the game such as which weapons in a mod are allowed, and how fast they reload and many other parameters which have huge impact on the game play.
NiL (recursive acronym for NiL Isn't Liero) is a clone of Liero, which runs on Linux and Windows and is released under the terms of the GNU General Public License. NiL is not, like Liero, limited to two players as it has support for an infinite number of players over a TCP network. It was met with considerable enthusiasm in the Linux gaming community.
The project was initiated by Flemming Frandsen in winter 1999 after he had stumbled across Liero, which he liked so much that he decided to reimplement it under Linux. He abandoned the project however five months later due to being too busy for it. NiL was then dead until the beginning of 2004 when the current maintainer of NiL, Christoph Brill, found out about the project and took over. Thereafter Daniel Schneidereit joined the project as well, but soon left. Other contributors included Nils Thuerey, Harri Liusvaara, David Hewitt and Phil Howlett.
Development however proceeded slowly as the project's source code became almost unmaintainable and NiL was lacking developers. By mid-2005 Alexander Kahl joined development, convinced Christoph to start over and re-think the whole concept of NiL, as the other Liero clone Gusanos already existed at that time. Development seems to have stopped around mid-2006.
- Liero Review at Home of the Underdogs
- Liero Wiki: MoleZ[dead link]
- official Liero wiki[dead link]
- official Liero wiki about Liero 1.33[dead link]
- official Liero wiki about modability[dead link]
- See the changes.txt file in Liero 1.34 or newer.
- James Murff. "Freeware Friday: OpenLieroX". Big Download. Game Daily.
- "OpenLieroX review". LANThrax.
- Liero review with side note about OpenLieroX
- Liero Xtreme entry in official Liero wiki[dead link]
- eGamer about OpenLieroX
- Ohloh statistics of OpenLieroX
- Czech review of OpenLieroX
- Change log of all OpenLieroX releases
- Webarchiv of original release post of Jason Boettcher
- Original post by Jason Boettcher
- Notes of original source release
- Official OpenLieroX homepage
- Open-source, networkable shooter has Linux gamers buzzing by Lee Anderson, April 12, 2000, CNN