  GaAs/AlGaAs quantum dots grown by in-situ droplet etching and nanohole
infilling offer a combination of strong charge confinement, optical efficiency,
and spatial symmetry required for polarization entanglement and spin-photon
interface. Here we study spin properties of such dots. We find nearly vanishing
electron $g$-factor ($g_e<0.05$), providing a route for electrically driven
spin control schemes. Optical manipulation of the nuclear spin environment is
demonstrated with nuclear spin polarization up to $60\%$ achieved. NMR
spectroscopy reveals the structure of two types of quantum dots and yields the
small magnitude of residual strain $\epsilon_b<0.02\%$ which nevertheless leads
to long nuclear spin lifetimes exceeding 1000 s. The stability of the nuclear
spin environment is advantageous for applications in quantum information
processing.
