I want to mention a few things of Scid that I love, and that I don't think everybody knows. When I have time.
First thing: THE CLIPBASE.
This is a complete, temporary database. Say, you have a huge database, and you use it for a lot of opening statistics, the tree window, et cetera. But now you only want to do this for games where Kasparov played 1.d4.
Search for header "Kasparov" as white. Play 1.d4, search for "Current position", using AND (restrict filter). Now you have selected all Kasparov's 1.d4 games.
Now open the Database switcher (ctrl-D). You'll see in your main database that you have some number of games of the total selected.
Now you can drag those games into the clipbase. Say the number is 150/20000, then click on the 150 and drag it into the clipbase.
Click on the clipbase to switch to it. Now you can use the tree, et cetera, but just on the selected games!
Sounds complicated but really isn't. And it's extremely powerful.