Combinations and endgame studies
Tactically gifted players are not only good at calculating variations - they know and recognize patterns. If you have seen a certain tactical theme once, it is much easier to spot the next time.
Here is a collection of 300 combinations on 25 pages. Some are easy, some are difficult and some are very difficult! There are sacrifices, pins, forks, interference, weak back ranks and much more. On most pages the combinations share one ore more themes.
There is also a collection of 89 endgame studies by the Platov brothers. Endgame studies are composed problems and the task is not to find a mate in X moves, but to either win or draw. Studies can be pure art and always have a surprising twist.
All problem pages are HTML/JavaScript made with Palview. You can try to find the right solution 3 times before it is revealed. Making a move/guess is simple: just click on the piece you want to move and then click the target square. Once the solution has been revealed you can still move (kibbitz) the pieces this way.
The Platov studies can be downloaded as PGN at Hull Chess Club