In order to study collective instabilities in symmetric nuclear matter, a simple phenomenological nucleon-nucleon finite-range potential with three adjustable parameters is proposed. The three parameters are the attractive strength, the attractive range, and the (zero range) repulsive strength. The potential reproduces the binding energy, equilibrium density, compressibility modulus, and the effective mass of nuclear matter, as well as the binding energies of ${}^{4}\mathrm{He},$ ${}^{16}\mathrm{O},$ and ${}^{40}\mathrm{Ca}.$ The latter conditions are crucial for preventing spurious ``quasicrystallization'' effects in nuclear matter. With this potential and a $(2+1)$-D deformed oscillator basis, variational Hartree-Fock calculations extending over the configuration space of the lowest 55 orbitals were performed for spin-zero, isospin-zero light nuclei up to $A=80.$ Large ground-state deformations and exotic nuclear shapes were found for many nuclei. Implications for their rotational spectra are discussed.