SCID vs. PC is the most fully-featured non-commercial chess program available. It is a very good and very fast database program similar to Chessbase. Download it direct from SourceForge
It there is also a lot of other valuable stuff it can do. If you are interested in making your own opening book, either to use on your computer with an engine or to print out a hard copy, SCID is a great program.
You can use it to produce an opening report that displays all kinds of facts about an opening. Information like which games that reach the position and moves played from the position. You can see if the opening is becoming popular, if it gives a lot of draws, and what transpositions are possible, etc. etc. The Positional Themes section reports the frequency some common positional themes e.g. an isolated QP.
Finally, there is the theory table, i.e. the ‘book.’ Here’s a sample of what you get for the opening book: