In recent month, updated the awesome Chess Gambiteer (open source) package (and gambits
in the polyglot book) again. You can get this free chess training software at:
Chess Gambiteer
(being open source, it's completely free (suitable for chess training).
Ofcourse you also can buy the GM Alterman video series:
GM Alterman gambit videos
but playing around with with the Chess Gambiteer package (play against an engine where
you can set the strength in Elo) or watch mastergames with gambits, based on Winboard
and without one combined GUI but simple double clicking on the .bat files should be easy
enough (for most users, and then there is a readme.txt as well ofcourse).
As GM Alterman states (in his book with White gambits), players at lower levels (than GM)
learnmuch more from playing gambits, especially tactics (but also attacking plans) than
simply parroting positional GM games (eg. Ruy Lopez, or Slav). In the old days of
chess it was thought by many players (including Gm's) that you can build up a positional
advantage with White, if you choose the 'best' opening moves. This turns out to be not 100 pct
solid, if Black defends well, also knowing such lines, you can't get a fundamental advantage
in the game (for top engines at longer time controls the end result is draw).
Thus playing sharp (often gambit) lines, especially those you know, is a better way to
induce tactical opportunities or exploit possible tacticial mistakes of your opponent in the
game; whereby in blitz it often doesn't matter how sound the gambit is (in the above Chess
Gambiteer package, the gambits in the big book are quite sound, and in the small
(Polyglot) opening book, reasonable sound. And when playing against a weakened engine,
which plays such sound gambits, you first learn defensive skills and then also by learning
those gambits for yourself, you can also practice those gambits against the comp (or online
opponents eg. on chess.com or lichess.org).
Good luck!
Nb in recent two months updated the content of some gambits in my educational book about
chess openings (link below), especially the Smith-Morra. Compared to known theory (and
historical games). It should be now again a higher quality, of importance for those
intermediate players who may choose to play gambits e.g. in blitz or rapid.
Edition 2.04 (July, 2024):
Kindle version of the book
In general, talking about modernized opening theory (as result of the Nnue engines), besides some recent opening books with 'Modernized' or 'Revisited' in the title as from Thinkers Publishing in Belgium, i don't know of any other chess opening books which is dealing simultaneously with all new theory at once (which i've done by chosing an optimal repertoire, at two levels, intermediate or advanced). You can buy Chessbase 17 ofcourse, for 190 $ or so, but for intermediate players this book (with lots of diagrams) should give sufficient info for opening study at such levels. And it's a lot cheaper too :)