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Monorail puzzles are a kind of logic path puzzle, based on Round Trip Puzzles, as presented in Glenn Iba's book "Round Trip Puzzles" (see Glenn Iba's Home Page).
The puzzles also appear as "Grand Tour Path Puzzle Applet" on my home page. You can try them out here: Grand Tour Page
The book Round Trip Puzzles and the Grand Tour Puzzle Applets feature many examples of both Square and Hex path puzzles. Monorail for iOS and Android each have a total of 880 puzzles available in various sizes, shapes, and difficulties.
Check out Glenn's Expanded Book Intro (online only) with in-depth analysis and solving strategies
Click on more Monorail Round Trip puzzles for an ever-expanding list of sources.