OCTOCAM is an 8-channel VIS-IR (g to K-band) simultaneous imager and medium-resolution spectrograph proposed as new workhorse instrument for the 8m Gemini telescopes. It also offers additional observing modes of high time resolution, integral-field spectroscopy and spectropolarimetry, making it a very versatile instrument for many science cases in the 2020ies. A special focus of OCTOCAM will be the detection and follow-up of transient sources such as gamma-ray bursts, supernovae, magnetars, active galactic nuclei and yet to be discovered new objects, delivered by large-scale surveys like LSST available in the 2020ies. The diverse nature of transients will require the full range of OCTOCAM capabilities allowing more information in very short time about the source than with any other current instrument and adaptable almost in real time. Another main science topic will be to probe the high redshift Universe and the first stars for which OCTOCAM will be highly suited due to its wide wavelength coverage and high sensitivity. However, OCTOCAM is also suited for a large range of other science cases including transneptunian objects, exoplanets, stellar evolution and supermassive black holes. Our science team comprises more than 50 researchers reflecting the large interest of the Gemini community in the capabilities of OCTOCAM. We will highlight a few important science cases demonstrating the different capabilities of OCTOCAM and their need for the scientific community.