Linked from
The 11 pages that link to Free group, each with the reason it gives.
Cayley graphRelated: Its Cayley graph is a tree, making it a basic model.
FunctorRelated: The free-group construction extends maps of sets to homomorphisms of groups.
Tits alternativeBroader topic: The other outcome is a free subgroup on at least two generators.
Andrews–Curtis conjectureRelated: Balanced presentations encode relators as words in a free group.