Open sourced tactical puzzle sets

I've taken a subset of the Lichess puzzle database and sliced it in ways you can't do in Lichess itself.

For example:

* Pawn forks
* Mates in one with at least 10 checks but just one mate
* Two move pins rated 1400-1500

You can see the puzzles here and download the data on github if you want to do your own thing.

My puzzle trainer also lets you redo only puzzles you got wrong, or got right too slowly, which might be useful for people too.

I've chosen sets that interest me, but let me know in the comments if you want others.