Simply brilliant!
Links directly to PGN Mentor & The Week In Chess for access to literally millions of games to build a database with, and you can import your own. Easy navigation of bases (player, year, event, ECO or combinations of those & other parameters) & a boat-load of various analysis & search functions including endgame tablebases. Also ability to create custom opening books for stockfish to use from databases is a big plus!
If you’re serious about chess, or want an easy to use, stable program for OTB prep, this is probably all you’ll ever need. Highly recommended.