He patented his namesake in the Sicilian, which Nimzovitch often employed as an anti-Sicilian system, when Nimzo wasn't also toying with the Rossolimo (the Variation) before Rossolimo (the Master) came along.

His Alapin Opening is suspect to say the least, but the similar 1. e4 c5 2. Ne2 is an interesting idea, something Bronstein played occassionally to good effect:

Bronstein vs Psakhis, 1981

When Queenabber played Alapin's Opening (1.e4 e5 2.Ne2), Bronstein asked in awe, "Did you know Alapin?"

Minev gives an overview over some of Alapin's opening ideas and forgotten or good chessgames.

Some excerpts:

<Sicilian Defense
His line with 1.e4 c5 2.c3, practically a new opening in his day, is now very popular. Batsford Chess Openings (solely!), the "record holder" for launching new and unjustified opening names, calls it the Alapin-Sveshnikov. However, I must mention that in Alapin's day this line was played by Alekhine, Tartakower, etc., and at that time nobody added any other names to Alapin's variation. As for the development of new and interesting ideas in Alapin's Sicilian line, I would give much more credit to Adorjan and Nunn than to Sveshnikov.>

<King's Gambit
Here there are many continuations associated with Alapin's name. Probably his most interesting idea is that the Falkbeer Countergambit is a dubious defense for Black. As far as I know, he analyzed and introduced into practice for White the following variation: 1.e4 e5 2.f4 d5 3.exd5 e4 4.d3 Nf6 5.dxe4 Nxe4 6.Nf3 (! Alapin) 6...Bc5 7.Qe2 (! Alapin). Even now this line is considered to be White's best.

After 7...f5 8.Nc3, ECO (C 32, note 77) gives 8...0-0 9.Nxe4 fxe4 10. Qxe4 Bf5 with an advantage for Black, and claims that the author is Keres.

This is unfair! This analysis was published by Alapin in "Monde Illustre" (France) in 1903 and reproduced in "Wiener Schachzeitung". Keres was not even born at that time!

I will present Alapin's original analysis further, because it is not mentioned in the opening guides: 11.Qc4 Nd7! 12.Bd3 Qf6! 13.h3 Rae8+ 14.Kd1. Assessment: unclear. Black has plenty of attacking possibilities, but White has two extra pawns.>

Minev also mentions a match against Tarrasch played at the end of 1902 and the beginning of 1903 (I'll submit the three games he gives). Alapin won the match but lost the battle.

Minev: <Was there an Alapin ? Tarrasch match? Officially such a contest is not mentioned in recent chess history. But in 1903/4 many newspapers and chess magazines were involved in a dispute over whether the nine games played between these two in Monaco and Marseilles, at the end of 1902 and beginning of 1903, were match games (as claimed by Alapin), or friendly games (as claimed by Tarrasch).

The games were played with a clock and a normal time control. From the evidence available to me, this was probably some sort of training match, with some pre-conditions - the games, for example, were to be played without spectators, and (probably) the score was not to be released. But a Belgian newspaper published the score anyway: +4, -3, =2, in favor of Alapin.

Tarrasch was furious and used bitter, insulting words against his opponent. Alapin's answer was more polite, making the point that he had nothing to do with the Belgian publication. He also showed a great deal of satisfaction in the fact that at least Tarrasch did not deny the score.

The result of this dispute was unfortunate for Alapin. After the furor, the German chess press (with Tarrasch and Mieses in the lead) virtually ignored Alapin's existence for years.>

To quote Edward Winter: <We note that St Petersburg was specified in the ten-line obituary of Alapin in the October 1923 BCM, page 374, on page 333 of Schachjahrbuch 1923 by L. Bachmann (Ansbach, 1924) and in a number of other publications of the time.>