I found this site which has download links to all of the best free openings books. One very interesting one is Chessmotor Attack.ctg (No.9 on the list) which I had not heard of before. I downloaded and tested it on the Playchess server and it looks strong.
My works: http://www.chesspraga.cz/spikebook.htm - main *.scb (spike) and *.bin (polyglot), other *.ctg (ChessBase), *.bok (Sjeng) and *.dat (Romichess)