The following is largely a documentation of the methods I used during my longtime partnership (1998-2011, with a few gaps) with Michael Schmahl. Most of the individual conventions can be used in other systems, but whether they are appropriate depends a great deal on your partnership style.
When asked what system we played, we answered, "we speak Standard American with a thick Polish accent." This was because several of our toys (our treatment of second round bids after 1m-1M-1NT among others) were inspired by the Polish Club as described by Greg Matula's 1994 book.
Like most modern tournament systems, ours had a natural basis, but with enough conventions heaped on it that it was a fairly long way from a simple Goren-type standard. We recognized most of the same problems with old-fashioned standard as the 2/1 authors do -- we simply disagreed with how 2/1 solved them. Our system was, in some sense, "the same distance away from SA as 2/1 is, but in the opposite direction" -- or at least in a perpendicular direction. For instance, we rejected Drury over 3rd seat openings. Instead of being tempted to open 9-counts in 3rd seat, we opened 11-counts in both 1st and 3rd, and our system included several ways to escape at the partscore level with 11 facing 11.
Among the conventions in common modern usage which we did use in their published form were Jacoby transfers, Lebensohl (over 1NT, over weak twos, and over reverses), negative doubles, and the Unusual NT. Among those which we used with modifications were inverted minor raises, Bergen raises, splinters, Ogust, support doubles, and the Sandwich NT. Among those which we rejected after due consideration were Drury, Puppet Stayman, Namyats, 1NT Forcing, Jacoby 2NT, Michaels, and Roman Keycard Blackwood.