The Danube Gambit is similar to the Benko Gambit or Blumenfeld Gambit. You play 3...b5 in order to develop your Bishop to g7 with tempo. If White accepts you get a couple of things for your pawn.
The first thing is quick development as already mentioned. White's d5-pawn also loses a solid defender and will be the subject of attack from your forces.
Your game plan is clear as your will bear down on d5 and attempt to break White's center. White will quickly play e4 to re-establish support for d5. This move will also blunt the g7-Bishop on the long diagonal. Your game will develop on the Kingside as you play to undermine White's pawn chain on e4 and maybe f3.
Chicago Gambit - 1.e4 e5 2.Nf3 Nc6 3.Nxe5 Nxe5 4.d4
The Chicago Gambit is an early Knight sacrifice that is dubious to say the least. Everything starts off sensibly enough with 1.e4 e5 2.Nf3 Nc6. At this juncture you can play a perfectly sane move like 3.Bc4 or 3.Bb5. Or you can play something crazy.
The crazy move here is 3.Nxe5 Nxe5 4.d4. You give up a Knight for a pawn. This allows you to chase the Black Knight around the board a little bit. You will take a development lead. This plan allows you to open up diagonals for your Bishops while Black keeps his Knight safe.
This gambit should not work with longer times on the clock. Black can keep the piece and has time to solve his development deficit without too much difficulty. It may be an asset in blitz play against a startled opponent who can't think on his feet.
The Latvian Gambit got it's name when it was extensively analyzed by some Latvian players early in the 20th century. It is considered unsound at the highest level because perfect or even solid play gives White a better game than Black.
However there is a flip-side and it's this. The Latvian Gambit is extremely complicated and has lots of possible lines, many of these leading to promising situations for Black.
Many players below master level and indeed some masters are not familiar with the maze of variations that arise from this gambit so it could be a useful weapon in your arsenal and you may be able to score some good victories with Black using it's variations.
The Lobster Gambit is a countergambit you can use as White against the Latvian Gambit. Your normal choices against the Latvian are accepting with 3.exf5 or the alternative capture, 3.Nxe5. The third conventional option is declining with the simple developing move 3.Nc3.
Many would say that Black is crazy to even play the Latvian. They say you can guarantee yourself the upper hand just by sticking to the established opening principles. Simple, straight forward play, nothing fancy will expose Black's reckless conduct.
You could do that or you might remember that sometimes you have to have fun in life. You can return Black's crazy with some crazy of your own. 3.g4 is the Lobster Gambit. If Black accepts it (3...fxg4), your center is relieved and you may gain the initiative. If he takes on e4 instead, you may be the one under pressure.
The Colorado Gambit is a great way to shake White up when he plays 1.e4 against you. You can avoid passive positions arising from sterile interpretations of the Ruy Lopez or the Sicilian.
I say this not because I think that these two openings are sterile, I don't. Both of them actually contain lots of potential for Black to reach stimulating scenarios. You can only get the most out of these openings through a lot of study. You must learn the deep conceptual ideas behind these openings to avoid tripping up in their sharp variations.
The Colorado after 1.e4 Nc6 2.Nf3 f5 may have a less challenging learning curve. It gives you the chance to gain a big center as Black against 1.e4. This alone is remarkable. Then there are all those juicy traps you can spring on White.
The Boden-Kieseritzky Gambit is found in the Petroff Defense. It's a resource you can put into play with the White pieces to gain some leverage against the Petroff.
The move 3.Bc4 sets the Boden-Kieseritzky in motion. Black takes on e4 and instead of 4.Nxe5 in classic Petroff style you will develop with 4.Nc3. Black will take on c3 and you will recapture with the d-pawn. Then Black plays 5...f6 to solidify his center and hold his extra pawn.
The resulting position leaves you with two developed pieces to none and the move. You can use this to develop a third piece. You also have an open center and can complete development without hindrance. Black will have to move one more pawn to get his light square Bishop out.
The Cochrane Gambit is an ingenious sacrifice that blows a hole in the Petroff Defense. Black employs this defensive system to create an almost impenetrable fortress from where you will find it difficult to win.
John Cochrane tried this unlikely looking sac in 1848. Top GMs are still known to use it in these modern times. What do you get for your Knight then after Black replies with 4...Kxf7.
First you get two pawns but more importantly you trap the Black King in the center. It is also a center where you will have a fearsome rolling pawn mass against Black's decimated center. You will sweep Black's pieces aside as you smash through the center to reach his King.
The Locock Gambit also in the Petroff Defense arises after 1.e4 e5 2.Nf3 d6 3.d4 Nf6 4.Ng5 h6 5.Nxf7. Again the Knight is sacrificed on f7 just as in the Cochrane Gambit and many of the same themes are revisited.
Again White traps the hapless Black King in the center where he and the other Black pieces will struggle to complete development. They are caught in the headlights of a rolling pawn mass and White pieces that effortlessly find beautiful posts from which to attack.
You will starve Black for space and his lack of connectivity and mobility is exacerbated by his King tripping over himself in the center. By the time Black has managed to develop somewhat it is clear who rules the center and who has the better pieces.
The Lopez Countergambit is a dynamic version of Black's Philidor Defense. You are trying to create an aggressive and imposing pawn formation stretching it's tentacles into White's territory. You then organize your pieces behind the pawns, planning your attacks in this way.
White will clearly respond to this game plan. He will target your advanced pawn center. He will try to smash your center and invade with his pieces. He then hopes to put your undeveloped pieces to the sword.
White develops his pieces as you build your center. Watch out for a piece sacrifice to break open the center. The game will hinge on the battle for the Black center.
The Philidor Countergambit is a way to ruffle White's feathers when you're facing a 1.e4 kind of attack. 3...f5 can be a shock to the system and most likely not what White was expecting. Normally he be prepared for something like 3...exd4, 3...Nf6, 3...Nd7, 3...Bg4 or even 3...Nc6.
3...f5 takes some courage to play. After all you're really weakening the light squares around your King who is no closer to castling. The a2-f8 and h5-e8 diagonals are now both open highways to your King.
If you get something passive from White like 4.Bd3, 4.Bg5 or 4.Nd2 then your move has paid off with a good position. However, better more testing moves, like 4.dxe5 or 4.exf5, breaking the tension, or calmer developing moves like 4.Bc4 or 4.Nc3, could put you on the back foot.
The Ponziani Countergambit is Black's most violent way of treating White's Ponziani Opening. White plays 3.c3 in order to support the later d4 push. As Black you have a few very playable options to answer 3.c3.
The three Main Lines in this position are 3...Nf6, 3...d5 and 3...d6. These continuations account for the vast amount games that reach this position. The Ponziani Countergambit, 3...f5, is the most important sideline. It can have a powerful psychological effect.
White will usually play 4.d4 here. This is answered by 4...fxe5. 4.d3 is another less popular way to decline, played to hold the e4-pawn. Here 4...Nf6 is the usual reply. White can also accept the gambit with 4.exf5 although this is also a sideline. You will push the e-pawn to kick the Knight if you get this move.
Capablanca - Marshall (New York, 1918); The original and most infamous Marshall Gambit, White wins with 36.Bxf7+.
More and more we see how supposedly positional openings do also have the potential of giving rise to tactical ideas and plans. It's never bad when you learn an opening to know of the gambits available among it's variations. You never have to use them but when the chance arises they can be great options to have.
You may have been cheered to find that some of these goodies are actually sound and safe lines that can give you at the very least a playable game. Of course you're hoping for the mistakes from your opponent that will give you so much more.