Commercial: Chessbase is the obvious choice and the mobile app is something like $9. Millions of games, the Fritz engine plus any UCI engine like Stockfish or Komodo can be used. Free: SCID or SCID on the go for mobile are good options. Personally I just use Droidfish and PGN files. I have different collections by player, event and opening. It's a bit more cumbersome than a database program but it works for me.
Choice of single chess software to use
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I'm trying to choose a chess program to get, and I see that there are a number of options out there, including free and commercial programs. Sometimes I make use of apps, websites and different sources, but I'm looking for a somewhat complete package including at least a GUI, an engine and a database system. From the several discussions I read online I understand I could get different best options for the different uses, but I would prefer to get a single software. My question is: if you had to choose from the available chess programs a single one to use for the rest of your life, what would it be and why?