We here report an optical system for live 3D microscopy that we call the Multifocus 25-camera microscope (M25). M25 is a new design for aberration-corrected multifocus microscopy (MFM) that employs the latest generation of small, fast and sensitive CMOS cameras. Each of the 25 focal planes is captured on one of the individual cameras, enabling truly simultaneous 3D recording at >100Hz. M25 is built from a combination of custom manufactured diffractive Fourier optics elements and off-the-shelf components. We are employing M25 to study neural circuit function in small model organisms including C. elegans, Drosophila, and fish.