The compact ORS-Mini Ultrastable Laser System for field applications and OEM integration delivers ultra-narrow linewidth laser light with excellent frequency stability. A high-finesse Fabry-Pérot cavity serves as reference for a CW laser. The 5-cm cubic cavity spacer from ultra-low expansion (ULE) glass is operated in vacuum at zero thermal expansion. Acoustic shielding allows for excellent performance even in rough laboratory environments. Rigid mounting of the cavity ensures portability without realignment of the optical paths.