Opening Trainers

Good Morning All,

I have been playing chess for years, but have just recently begun to take the study of chess more seriously.

In the past, I studied tactics and middle game principles, with a cursory study of king and queen pawn openings.  The cursory study was just enough to get me through in casual games of chess.

Now I am finding that my current regular opponents are a bit more sophisticated and studied, particularly with respect to the opening, and so I would like to increase my knowledge as well.

I have studied Seirwan's book on the subject, and I found it very useful.

Can anyone recommend a good piece of software to use as an opening trainer?

Thank you in advance,

David