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

Best Chess Openings for White: Full Guide - 365Chess

What Is Tempo in Chess?

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: Chess tactics on the App Store

New opening trainer features

The biggest chess databases - Chess Forums

Why does chess tempo fail at random; what is the biggest free database online that is reliable - Chess Stack Exchange

Keep the tempo in chesstempo (2300-2400)

Reached 365 days on r/chesstempo! Easy even if you usually leave standard puzzles overnight. No need 2nd account or griefing. Just do blitz on old site (old.chesstempo.com/chess-tactics.html) and standard on new site.

Chess Tactics Puzzle Training : Chesstempo.com Tactics and Puzzle Training review (Chessworld.net)