Types of Puzzles: Six Groups by the Material You Work With
Word, number, picture and spatial, physical piece, pure logic and chessboard puzzles: what each type of puzzle uses and how to begin.
Riddle10 blog
Articles about chessboard puzzles
What Makes a Puzzle Hard? Search, Outcomes and Hidden Rules
Four things make a puzzle hard: a huge search, tests that reveal little, long solutions and hidden constraints. What the research shows for each.