Two central features of dilute Bose-Einstein condensate (BEC) gases are the tunable nonlinearity with respect to the bosonic field operator and the small depletion. These allow for the investigation of different classes of phenomena, ranging from the existence of persistent currents in toroidal traps to the creation of multiparticle entanglement. The latter can be exploited for interferometric measurements with sensitivity up to the ultimate limit allowed by quantum mechanics. We’ll discuss some recent results along these lines after a short introduction on the physics of trapped BEC gases.