|The following is based on Fallout 3 cut content and has not been confirmed by canon sources.|
Fallout 3 cut content refers to content in Fallout 3 which was cut from the final version of the game. Most of it can still be found in the game files but is inaccessible from within the game. The equipment can still be obtained by use of console commands though.
The game files contain the remnants of a main quest called "Infiltration". According to its numbering, it was supposed to take place in between The American Dream and Take it Back!. In it the player would have had to retrieve a prototype's energy source from Rivet City, presumably to power up Liberty Prime. In the final game it is simply stated that Dr. Li and Scribe Rothchild managed to restore its energy source but is not specified how they accomplished that.
The game files also contain the name of another main quest called "Last Rites", but nothing beyond that. According to its numbering, it was supposed to take place after Take it Back!. It might have later been used as the basis for the Broken Steel add-on.
At some stage in development, the Wasteland Survival Guide contained another quest stage. The player's objective would have been to print the books at Hubris Comics and return them to Moira (who at this point was apparently still called "Lea") as part of the work on the last chapter. This makes Moira's remark in the final game that it's cynical of the player to assume she would require such a dangerous task of him/her doubly ironic.
Some remaining dialogue in the games files reveal that there was another radio station planned at least temporarily, presumably broadcasting from Tenpenny Tower and featuring truisms from Allistair Tenpenny akin to President Eden's motivational quotes.
Numerous armors and weapons are to be found in the game files which were cut from the released version of Fallout 3 such as Wanda, the Law Dog or "Robo-Thor" Armor. Most of the weapons are unique variants of regular armament and do not have an equivalent or replacement in the final game. For example, there is no unique Assault Rifle in the Capital Wasteland.