The structural, electronic, dynamical, and optical properties of a group of 2D germanium-based compounds, including GeC, GeN, GeO, GeSi, GeS, GeSe, and germanene, are investigated by employing first-principles calculations. The most stable structure of each of these systems is identified after considering the most probable configurations and performing accurate phonon calculations. We introduce a new phase of germanene, which we name the tile germanene, which is significantly more stable than the known hexagonal germanene. We apply the modern modified Becke-Johnson and DFT1/2 schemes to obtain an accurate band structure for the selected 2D materials. It is seen that GeO and GeC exhibit the highest bandgaps of >->3 eV in this group of nanomaterials. Moreover, we argue that, in contrast to the semi-metallic nature of hexagonal germanene, tile germanene is a very good conductor. The band edges of our semiconducting 2D materials are accurately aligned to the vacuum level to address the potential photocatalytic application of these systems for water splitting and carbon dioxide reduction. The optical properties, including dielectric functions, refractive index, reflectivity, and loss function of the samples, in the presence of excitonic effects, are investigated in the framework of the Bethe-Salpeter approach.