A set of lecture notes affectionately known as “Joe’s Little Book of [these systems]” is a companion to Polchinski’s textbook on these systems. Considering all surfaces of genus one under the Polyakov path integral constitutes the one-level analysis of these systems, whose simplest invariant model is the Nambu–Goto action. (15[1])These systems (15[2])trace out worldsheets in spacetime, (15[2])and their boundary conditions create D-branes. Ed (15[2])(*) Witten combined several related theories of these systems (-5[1])with supergravity into the 11-dimensional (10[1])M-theory, providing a unification of quantum mechanics with general relativity. Particles are envisioned as vibrational modes of these systems in those namesake theories. For 10 points, name these one-dimensional systems that form the basis of an unverifiable theory of everything. ■END■ (10[1])