Chess Opening Theory/1. e4/1...e5/2. b3

= Charles' Opening =
Charles' Opening is an unusual chess opening named after the British chess player and writer (1886–1945.) Although this opening is rarely used, Vilmos Nogrady (as White) played it with mediocre success, tying with Meszaros Gyula in 1993.
Description.
Charles' Opening is offbeat, but perfectly playable for White. It is mainly used to avoid highly theoretical lines such as the Ruy Lopez or the Scotch Game: Schmidt Variation, or to surprise the opponent. White intends to play Bb2 soon. After 2...c7-c5, the position is similar to an Anti-Sicilian.
Charles' Opening incurs a couple of problems for White. First, it delays the development of a minor piece, disallowing an early castle for White to bring their king to safety. The other problem is that it removes the advantage White has going first. 2. b3 delays the development of another piece with something like 2. Nf3 or 2. Bc4, instead planning to develop their dark-squared bishop to b2, which gives black more time to develop.
It is relatively easy for Black to equalise in this opening, for example, 2...Nf6, 2...Nc6, and 2...Bc5 all equalise, although Black should be careful to avoid a quick Bb2 and Nf3, putting intense pressure on the pawn on e5.
Main variations.
After 1. e4 e5 2. b3, the most important continuations are:
Main line: 2...Nf6.
In the main line after 2...Nf6, White has two major options. Either 3. Bb2 or 3. Nf3 offers White good chances for an equal game.
Classical Variation: 3. Bb2.
The classical variation of the Charles' Opening is the most analyzed variation. After 3. Bb2 Black has 3...Nxe4, 3...Bc5, or 3...Nc6. After 3...Nxe4 play usually continues 4. Qe2 d5 5. Nc3 Bf5 (Black does not play 5...Nxc3 because they wants to hang on to their pawn advantage. Black would lose his pawn advantage after something like 6. Qxe5+ Qe7 7. Qxe7+ Bxe7 8. Bxc3) 6. Nxe4 dxe4 7. Qb5+ Nd7 (once again the best move hanging on to the e5 pawn) 8. Ne2 (White develops his knight instead of playing 8. Qxb7 because Black can play 8...Rb8 9. Qxa7 Bc5 10. Qa4 O-O, where White is up a pawn but Black has a major development lead and White's queen is on the awkward a4 square. The computer sees this position -1. 90 for White.) 8...Rb8 9. h4?! (This move threatens to trap black's dark-squared bishop.) 9...h5 10. O-O-O. The "Stockfish Engine" says Black is slightly winning but that is only because of a complicated line after 10...c6. 3...Bc5 is probably the strongest move, since it quickly develops another piece and prepares to play O-O extremely early. After 3...Bc5 play usually continues 4. Nc3 O-O 5. Qe2 Re8 6. O-O-O a5 (a7-a5 is a very good move. It plans to weaken the queenside and break White's fianchetto with an eventual a5-a4) 7. Nf3 d6 (supporting his other central pawn and his developed bishop, while allowing his other, undeveloped bishop to develop) 8. d4 exd4 9. Nxd4 a4 10. Kb1 Nc6 11. Nxc6 bxc6 12. f3 axb3 13. cxb3 Ba3 (trading off one of his most active pieces in order to expose White's king even more) 14. Bxa3 Rxa3 15. Qb2 Rb7 (planning to eventually double up his rooks on the a file with Rea8). The final response to 3. Bb2 is 3...Nc6. After 3...Nc6 play usually continues 4. Nf3 Bc5 5. Bd3 O-O 6. O-O Re8 7. Nc3 d6 8. Na4 (planning to trade their knight for Black's active bishop while activating his bishop on b2) 8...Bg4 9. Nxc5 dxc5 10. a4 Nd4 11. Bxd4 cxd4 12. h3 Bh5. This position is very even. White plans to expand queenside with moves like b3-b4 and a4-a5; Black plans to clamp the center with move like c3-c5 and slowly maneuver his pieces to the kingside for an attack. Overall, the classical variation of the Charles' Opening is the most challenging variation against 2...Nf6. If a player likes lots of opening theory and wants a new weapon for their opening repertoire, the Charles' Opening: Classical Variation is for them. 
Wells Variation: 3. Nf3.
The Wells variation of the Charles' Opening is playable, but definitely not the best variation after 2...Nf6. The "Stockfish Engine" evaluates the position after 3. Nf3 -0. 86 for White. After 3. Nf3 Black has 3...Nxe4, 3...Bc5, or 3...d5. After 3...Nxe4 play usually continues
Fine Defense: 2...Nc6.
The Fine Defense often transposes to the Classical Variation of the Charles' Opening. For example, after 3. Bb2 Nf6 it is a line in the Classical Variation of the Charles' Opening. However, after 2...Nc6 White can opt not to transpose to the classical variation with 3. Nf3. 3. Nf3 can transpose to the Bishop's defense after 3...Bc5, but the best response for Black is to play 3...Nf6. After 3...Nf6 play usually continues 4. Bb5 Nxe5 5. O-O Nf6 (Black breaks the principle of not moving pieces multiple times in the opening to remove the threat of Re1, hitting the knight and, in the future, putting another attacker on the pawn on e5.) 6. Bxc6 dxc6 7. Nxe5 Bd6 (developing while attacking the knight) 8. Re1 (setting up a discovered check if they move their knight) 8...O-O (moving out of the discovered check) 9. Bb2. The Fine Defense is one of the weaker responses to the Charles' Opening; if you want an opening that is solid, yet can transpose to multiple other variations of the Charles' Opening, then the Fine Defense is for you.
Bishop's Defense: 2...Bc5.
The Bishop's defense was once used by Jan Sosna in 2018, where they beat Marvin Engert in a game. After 2...Bc5 White has two major options, 3. Nf3 and 3. c3. After 3. Nf3 play usually continues 3...Nc6 4. Bb5 Nge7 5. O-O Nd4 6. Ba3 (Ba3 looks like a strange move, but it has purpose. White plays this move looking to trade off Black's most active piece, their bishop on c4.) 6...Nxf3+ 7. Qxf3 Bxa3 8. Nxa3 O-O. It's hard to decide who's winning this position. White has a lead to development, but their pieces are awkward, with a bishop on b5, pinning nothing, and a knight on a3 that's only useful squares it can see is c4 and b5. 3. c3 is a move that intends to get a big center with an eventual d2-d4. After 3. c3 play will usually continue 3...d5 4. d4 exd4 5. cxd4 Bb4+ 6. Bd2 Bxd2+ 7. Nxd2 dxe4 8. Nxe4 Nf6 9. Nxf6+ Qxf6 10. Nf3 O-O 11. Bc4 Re8+ 12. Ne5 (where White's king is severely exposed and they will have to give up a pawn in order to castle after something like 12...Nd7 13. O-O Nxe5 14. dxe5 Rxe5). Overall, the Bishop's Defense, is one of the more challenging ways to beat the Charles' Opening and is a good tool to have in your opening repertoire.
Cincinnati Gambit: 2...f5?!
The sharp 2...f5, the Cincinnati Gambit, although somewhat dubious, was played a few times by 1989 Cuban chess champion IM Pedro Paneque Martin, where they once tied with Luis E. Valdes. It may lead to complicated positions and interesting endgames, e.g. 3. exf5 Nf6 4. Bb2 d5!? 5. Bxe5 Bxf5 6. Nf3 Bd6 7. Bd3 Bxd3 8. cxd3 (where White is a pawn up, but has doubled, isolated queen's pawns.) White has multiple ways to decline the gambit. 3. d4, 3. Bb2, and 3. Nc3 are all strong ways for White to decline the gambit. After 3. d4 play usually continues 3...Nf6 4. exf5 exd4 5. Nf3 (White doesn't play 5. Qxd4 because it leaves their queen exposed, allowing black to play normal developing moves like Nc6 while forcing the queen to move) 5...Bb4+ 6. c3 Bxc3+ 7. Nxc3 dxc3 8. Ba3 (White loses a pawn in this line, but has compensation since it's bishop has a strong diagonal on a3, which doesn't let Black play O-O) After 3. Bb2 Black plays 3...Nf6 (Black doesn't play fxe4 because of the deadly 4. Qh5+!!, followed by either 4...g6 5. Qxe5+ Qe7 6. Qxh8, or 4...Ke7 5. Qxe5+ Kf7 6. Bc4+ d5 7. Bxd5+ where black has to sacrifice their queen with 7...Qxd5 in order to not get checkmated or lose even more material) 4. exf5 Nc6 5. Bb5 a6 6. Bxc6 dxc6 7. Bxe5 Bxf5 (where White is a pawn up, but Black has a minor lead in development.) 3. Nc3 is the weakest way to decline the gambit. Play usually will follow with 3...Nf6 4. f4 exf4 5. e5 Ne4 6. Nxe4 fxe4 7. Qe2 d5 8. exd6 Qf6 9. Qxe4 Kd8 (Black doesn't play 9...Be6 because 10. dxc7 Nc6 11. Ba6!! where White has a major advantage of roughly +3. 75) 10. dxc7+ Kxc7 11. d4 Bd6 (In this position, Black is a pawn down and can no longer castle, but will gain a lead in development since White's queen is exposed so moves like Bf5 force it to move.) Overall, the Cincinnati Gambit is rarely played, but is an interesting opening that is laced with tricks and traps.