This site is available in both Italian and English and offers both tactical and endgame positions for study. From the site: 3400 positions (each file 100) which were primarily taken from actual played games. Each of the tactical combinations was either played or could have been played as a different variation. The tactical problems are graded by level of difficulty.
What I like is you do not need to solve these online or download a db so they can be used with a chess playing program. The problems open in a pdf book which you can then save, read on line or, best of all print. For example the section containing “very hard” problems opens up a 19 page pdf book with problems and solutions. If you want to open them all and print out a book, there’s even a pdf cover page! A very nice site.