Well I will start with the unsuccessful one first, which was the CCC-1 ("Coffin-Cutler Collaboration"). This was Bill Cutler's exchange puzzle and it was designed in collaboration with Stewart Coffin and based on Coffin's Design #177A. The CCC-1 was made by Coffin.
It's a packing puzzle and the object is to fit the 5 polyminoes (ranging from 4 to 6 units) into the tray. The puzzle came with its accompanying literature/explanation. I think both Cutler and Coffin knew that this was no easy puzzle so they also including a note containing a clue on how to solve it. But even with the clue, I was hopelessly lost and had to asked fellow Sinaporean puzzle collector/designer Goh Pit Khiam for help.
Goh is quite an expert on these sort of packing puzzles having designed many of them himself including the IPP33 award winning Dancing Shoes. Goh had earlier borrowed the CCC-1 from me and solved it rather quickly.
Like always, only with the benefit of hindsight after seeing the solution, I felt perhaps I could have done better with the CCC-1. Very difficult puzzle indeed (at least for me) and I think the solving aid provided is probably quite necessary. Definitely would be of much interest to packing puzzle enthusiasts, and since its a Coffin/Cutler puzzle, a great addition to any puzzle collection. If the CCC-1 could be made with exotic woods, even better still. As far as I can tell, the CCC-1 is not available commercially so the only source is from Bill Cutler.
I had much better luck with the Scott Elliot's Diamond Engagement Exchange Puzzle. Last year his exchange puzzle was "Join The Club". This year his exchange puzzle borrows the same theme as Join The Club with a similar solving method. Scott produced his puzzle via 3D printing.
Although the puzzle consists of only 2 pieces, getting them together still required some effort and experimentation. But once you find the correct " entry" point, the pieces slide themselves nicely into each other. The solution is actually quite easy once you figure out what to do and the solving becomes very repeatable; ust a couple of seconds is all it takes.
Diamond Engagement is one of those highly pocketable puzzles that you can easily take with you anywhere and have a play while waiting for someone, travelling on public transport etc to keep your fingers occupied. it is available for sale by PuzzleMaster of Canada for CA$24.99.