Textbook solutions

Algebraic Topology Allen Hatcher

Various solutions through chapter 3 (homology and some cohomology)

Basic Category Theory Tom Leinster

Solutions to assorted exercises from the whole book

Sheaves in Geometry and Logic MacLane and Moerdijk

Solutions to exercises and proofs of theorems in introductory topos theory

Algebraic Topology William Massey

A few solutions from the chapters over fundamental group and covering space theory

Theory of Computation Michael Sipser

Assorted solutions covering finite automata theory