  6D spinors with $Spin(3,3)$ symmetry are utilized to efficiently encode three
generations of matter. $E_{8(-24)}$ is shown to contain physically relevant
subgroups with representations for GUT groups, spacetime symmetries, three
generations of the standard model fermions, and Higgs bosons. Pati-Salam,
$SU(5)$, and $Spin(10)$ grand unified theories are found when a single
generation is isolated. For spacetime symmetries, $Spin(4,2)$ may be used for
conformal symmetry, $AdS_5\rightarrow dS_4$, or simply broken to $Spin(3,1)$ of
Minkowski space. Another class of representations finds $Spin(2,2)$ and can
give $AdS_3$ with various GUTs. An action for three generations of fermions in
the Majorana-Weyl spinor ${\bf 128}$ of $Spin(4,12)$ is found with $Spin(3)$
flavor symmetry inside $E_{8(-24)}$. The ${\bf 128}$ of $Spin(4,12)$ can be
regarded as the tangent space to a particular pseudo-Riemannian form of the
octo-octonionic Rosenfeld projective plane $E_{8(-24)}/Spin(4,12)=
(\mathbb{O}_s\times\mathbb{O})\mathbb{P}^2$.
