Hands Down the Best Puzzle Tool I've Used in 30 Years of Teaching Chess Classes! At the US Chess Academy we teach at most of the top schools in Manhattan, and Chessgo has quickly become our favorite resource for in-person chess classes.
We can instantly find puzzles on any theme (even "en prise" puzzles that are almost impossible to find elsewhere), swap out puzzles we don't like, and easily include or exclude answer keys. If there's a particularly challenging puzzle, such as a mate in five, we can click through the solution right on the puzzle before printing it out.
Sharath, the developer, responds to questions promptly and regularly adds improvements and new puzzle categories. We can even add our academy's branding to puzzles, which looks fantastic when students bring them home as homework.
I genuinely wish I'd had Chessgo for the past 30 years — it's that good.