Jacques Dixmier published two books of short stories in science fiction, L'Aurore des dieux (1993) and Le Septième arrhe (1995).
And one more co-authored with Alain Connes and Danye Chéreau: Le Spectre d’Atacama (2018); recently reviewed by @Gro-Tsen.
David Bessis published a novel (Sprats, 2005) and a "sentimental atlas" (Ars grammatica, 2006).
Recommended: Michèle AudinMichèle Audin, La Formule de Stokes, roman (2016);, already mentioned in this thread; gave me several fits of the giggles in the past hour.