Calculators and analysis utilities — free, no signup, each explained honestly by a grandmaster.
Free chess Elo calculator: your exact rating change after a win, draw or loss, plus win probability for any rating gap — explained by a grandmaster.
Paste a FEN or PGN and get the best next move, the evaluation and the top three lines from Stockfish, free and in your browser — with a grandmaster's guide to reading it.