  The Stoner instability remains a cornerstone for understanding metallic
ferromagnets. This instability captures the interplay of Coulomb repulsion,
Pauli exclusion, and two-fold fermionic spin degeneracy. In materials with
spin-orbit coupling, this fermionic spin is generalized to a two-fold
degenerate pseudospin which is typically believed to have symmetry properties
as spin. Here we identify a distinct symmetry of this pseudospin that forbids
it to couple to a Zeeman field. This `spinless' property is required to exist
in five non-symmorphic space groups and has non-trivial implications for
superconductivity and magnetism. With Coulomb repulsion, Fermi surfaces
composed primarily of this spinless pseudospin feature give rise to Stoner
instabilities into magnetic states that are qualitatively different than
ferromagnets. These spinless-pseudospin ferromagnets break time-reversal
symmetry, have a vanishing magnetization, are non-collinear, and exhibit
altermagnetic-like energy band spin-splittings. In superconductors, for all
pairing symmetries and field orientations, this spinless pseudospin
extinguishes paramagnetic limiting. We discuss applications to superconducting
UCoGe and magnetic NiS$_{2-x}$Se$_x$.
