Abstract: I will first briefly review the molecular gas content of early-typegalaxies. I will show not only that they unexpectedly harbour much cold gas, but also that it is the best tracer of the circular velocity, thus allowing accurate spatially-resolved dynamical mass measurements in galaxies across the Hubble sequence. Second, I will explore the use of molecular gas for studies of the Tully-Fisher (luminosity-rotational velocity) relation of galaxies to high redshifts. I will highlight the work done to establish local (z=0) benchmarks and will discuss the challenges posed by systematic effects when comparing nearby and distant galaxies. Third, I will demonstrate that CO can be used to easily and accurately measure the mass of the supermassive black holes lurking at galaxy centres. I will discuss substantial ongoing efforts to do this and present many spectacular new ALMA measurements, that open the way to literaly hundreds of  measurements across the Hubble sequence with a unique method. I will also hint at how the same data allow to study the spatially-resolved  properties of giant molecular cloud populations in non-local galaxies for the first time, providing a new tool to understand and contrast the  star formation efficiency of galaxies on cloud scale.