The G.E.C.K. (Garden of Eden Creation Kit) offers a set of mod tools for users to create custom content for Fallout 3. Check the G.E.C.K. wiki for instructions, help and tutorials.

"The G.E.C.K. provides the community with tools that will allow players to expand the game any way they wish. Users can create, modify, and edit any data for use with Fallout 3, from building landscapes, towns, and locations to writing dialogue, creating characters, weapons, creatures, and more."

Download the Fallout 3 G.E.C.K. Mod Tools (8.47 MB)
Check out all Fallout 3 downloads