Linked from
The 20 pages that link to Smooth manifold, each with the reason it gives.
Lie groupNarrower topic: It supplies the geometric structure underlying a Lie group.
Tangent spaceNarrower topic: Tangent spaces are assigned to points of these spaces.
FractalCompared with: Fractal boundaries can be too irregular to form smooth manifolds.
ManifoldBroader topic: Smooth manifolds provide the standard setting for differential geometry.
Tensor fieldNarrower topic: Its points are the locations where the tensor assignment is defined.
Morse theoryNarrower topic: Morse theory studies smooth functions defined on these spaces.
Symplectic geometryNarrower topic: Symplectic forms live on smooth manifolds.