Computer chess - Q&A

I thought I'd start a discussion/question thread on chess programs. "Cos I have a LOT of questions. But please feel free to put your own. A couple of mine first:

I have a chess.app on my Mac laptop. It's a good program for playing on your own against the computer, but I can't seem to save games. There is an option for saving the game as a pgn file, but once I've done that, I can't open it with ScidvsMac, which is now my default opener of pgn files. Is this a true pgn file, or a format that is basically different? I'm not surprised to find that the Mac "help" file doesn't give me any help at all, but in true Apple fashion sends me to a site that wants to sell me stuff.

Another question: When I watch the GMs do their videos on the chess.com site, what program are they using for the demonstrations? Is it available to the great unwashed like me?

Thanks in advance for your replies and questions. I've lots more but don't want to overburden the chess.com bandwidth.

Genghis