A series of actually hard puzzle books, so far sudoku, killer sudoku and some fiendish wordsearches that only use 5 letters per grid.

https://extremepuzzlebooks.com

A sample wordsearch is available as a pdf here: https://extremepuzzlebooks.com/assets/sample/extreme-wordsea...

I'm quite proud of this wordsearch concept as I've not seen it done before.

All the logic puzzles have an online solution to show step by step how you can complete them.

https://extremepuzzlebooks.com/walkthroughs

I've been working on the software to generate, test and verify these for a couple of years and finally built up enough puzzle stock that meets the difficulty requirements to properly launch.

Now the work is on every hackers favourite part... Marketing!