Totally Indescribable
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