derived smooth geometry
A zero locus of a set of polynomials is an affine algebraic variety; mimicking this situation Alexandre Vinogradov has introduced a geometric object related to systems of nonlinear differential equations, the diffieties. Closely related notions in various flavours of geometry are the crystals of schemes (Grothendieck), D-varieties (Malgrange), D-schemes (Beilinson, Drinfeld) and differential algebras (Ritt, Kolchin).
G. Cicogna, G. Gaeta, Lie-point symmetries in bifurcation problems, Annales de l’institut Henri Poincaré (A) Physique théorique, 56 no. 4 (1992), p. 375-414 numdam
L. Vitagliano, Hamilton-Jacobi diffieties, arxiv/1104.0162