As a past occasional maintainer of SAIL, I'll add my version of history: I believe the compiler originated as a class assignment for Jerry Feldman's compiler writing class. As noted, Dan Swinehart was one of the principal contributors. The addition of LEAP to SAIL was a direct result of Feldman's past work at Lincoln Labs. SAIL was used by everyone for everything at the AI Lab because of it's "kitchen sink" philosophy including the link to assembly language inside the language. Eventually, a source language debugger called BAIL was written by John Reiser. With the slow and steady decline of the PDP-10 and the ascent of Unix, SAIL went off into the sunset. [MWK,AIL]