MiniSat is a comparatively small SAT solver with documentation
(through the following paper). The first version was just above 600
lines while containing many then-desirable features (conflict-clause
recording, conflict-driven backjumping, VSIDS dynamic variable order,
two-literal watch scheme), and even extensions for incremental SAT
and for non-clausal constraints over boolean variables.
The current MiniSat v2 supports variable elimination style