Using a Jenga towerEdit
A Jenga tower is made of 54 wooden bricks, each three times as long as it is wide, and roughly one fifth as thick as its length. These blocks are stacked in eighteen levels, each made of three blocks side-by-side, with the blocks on each new level perpendicular to the blocks in the one below.
During a game, blocks are pulled out of the tower one at a time and then placed onto the top. This requires a certain amount of skill and a steady hand, but it is initially relatively easy (tiny variations in the manufacture of the blocks mean that some will be in the tower more loosely than others) and then becomes much harder and more tense as more blocks are removed, the weight and support structure of the tower shift, and balancing new blocks becomes increasingly precarious. Eventually, the tower will collapse.
While Jenga is the brand name and title of the game that first created the Jenga tower, it is often used as a generic trademark for similarly designed towers with the same purpose.
Jenga tower as a core resolution mechanicEdit
One of the main uses of a Jenga tower in a role-playing game is as part of a game's resolution mechanic (used instead of other randomisers like dice). If a player can pull a block and place it successfully on top of the tower, their player character has succeeded at what they were trying to do; if the tower falls, the player character has failed with potentially catastrophic consequences. Some games may also allow a third option for players to give up on pulling a block, in which case the character fails but not in a catastrophic way, or perhaps backs down from the attempt in the fiction.
Using a Jenga tower in this way is useful for games for which "failure" is rare (likely happening at most once in a game) but so significant that it would be life-changing for the characters and a climax for the story. The tower represents increasing tension in the story by increasing the tension among the group of players.
The first game to popularise the use of a Jenga tower as a resolution mechanic was Dread by Epidiah Ravachol, a horror game in which a pull is made every time a character tries to do something risky. When the tower falls, the character of the player who failed to make the pull dies or is otherwise removed from the game.
Another example with a different focus is Star Crossed by Alex Roberts, a romance game in which two player characters are attracted to each other but there is a compelling reason not to act on those feelings. A pull is made when one of the characters does something to increase their attraction, and when the tower falls the lovers act on their feelings. The number of blocks pulled by the end of the game will determine the outcome for the lovers in the story (doomed, triumphant, etc.).
Other uses of a Jenga towerEdit
A Jenga tower can sometimes be used in role-playing games as something other than a core resolution mechanic. For example, GM Alex Jaffe used a Jenga tower in a game of Dungeons & Dragons as a sort of prop to represent an overloaded merchant's wagon. Each brick represents a specific and individualised item on the wagon, with the names of the items written around the edges of the brick so that only part of the name can be viewed from any particular side. Players can pull bricks to represent their characters pulling objects out of the wagon to get a better look (or buy), but this is in the context of a social encounter with the merchants, whose willingness to help depends on the actions of the characters. If the tower collapses, then the tower of items collapses in the fiction as well, with all the consequences that entails.