  We explore quantum field theories with fractional d'Alembertian
$\Box^\gamma$. Both a scalar field theory with a derivative-dependent potential
and gauge theory are super-renormalizable for a fractional power $1<\gamma\leq
2$, one-loop super-renormalizable for $\gamma>2$ and finite if one introduces
killer operators. Unitarity is achieved by splitting the kinetic term into the
product of massive fractional operators, eventually sending the masses to zero
if so desired. Fractional quantum gravity is also discussed and found to be
super-renormalizable for $2<\gamma\leq 4$ and one-loop super-renormalizable for
$\gamma>4$. To make it unitary, we combine the splitting procedure with a
fractional generalization of the Anselmi-Piva procedure for fakeons. Among new
technical results with wider applications, we highlight the Leibniz rule for
arbitrary powers of the d'Alembertian and the K\"all\'en-Lehmann representation
for a propagator with an arbitrary number of branch cuts.
