The major contemporary competition for Schenkerian reduction theories of pitch space is what is known as "Neo-Riemannian" theory, or NRT for short. NRT begins from the notion that chords -- and by extension key areas -- can be understood as moves on a kind of chessboard of tonal relations, where each move is a tonal interval (most usually the fifth or fourth on one axis, and the third on the other). The effective "distance" between chords is mapped in two directions on a lattice-like "net" of such moves (in German: Tonnetz).
The power of NRT is encapsulated in the idea that the most common chess moves along this lattice will involve what is called "maximally smooth voiceleading," where common tones are preserved and stepwise motion of voices is preferred. The most frequently occuring transformations are labeled according to the system of 19th-ct theorist Hugo Riemann did, thus the name of the theory:
P = Parallel = C major - C minor = CEG - CEbG
R = Relative = C major - A minor = CEG - CEA
L = Leading tone exchange = C major - E minor = CEG - BEG
One can model quite complicated chromatic chord progressions by chaining these smooth transitions:
C major - Ab major = PL
C major - Ab minor = PLP
C major - Fb major = PLPR
If you are interested in learning more, you can check out the work of Richard Cohn, who is a Professor of Music Theory at Yale.