PokerTracker

Hi,
What is this and why does it list 100’s of players as ‘still playing’?

That is a Tournament Summary file written by PokerStars when a tournament is closed. When you are eliminated all remaining players are "still playing" - results are only known up to your finishing position. If you want to fill in the remaining results you will need to request the summary again from PokerStars after the tournament completes (which you can do from the Requests menu in the PokerStars lobby).