Chesstempo.com now has an opening trainer : r/chess

A Complete Guide On Tempo In Chess With Example!

Is Chess Tempo performance really that important? It seems like the correlation between it and OTB playing strength is quite weak. : r/chess

Chess Tempo mobile

Grandmaster Guide to Learn and Improve Chess Tactics

chesstempo - Chess Club

Tactics from the Old Masters - Chess Lessons

Chess Duels 1921 - 1924 : 127 Games Annotated by Alexander

The biggest chess databases - Chess Forums

Black is Back: Old Benoni

If tactics are so important to improving in chess then why isn't everybody a 2000+ rated player from just using Chesstempo? - Quora