A new two-dimensional carbon allotrope named twin α-trigraphyne monolayer is introduced in the present study and compared with α-trigraphyne monolayer. The structural, mechanical, electronic, and optical characteristics of α-trigraphyne and twin α-trigraphyne sheets are studied by density functional theory. The cohesive energy, ab initio molecular dynamics simulations, and phonon dispersion confirm that these sheets are energetically favorable and thermodynamically stable at room temperature. Both α-trigraphyne and twin α-trigraphyne, due to their porous structures, are more easily deformable than graphene. Calculations of the electronic properties indicate that both of the considered sheets are metals. In addition, the optical properties are investigated for incident light with parallel and perpendicular polarizations. The optical behavior of the sheets is found to be strongly anisotropic. For light parallel to the sheets, high optical constants and strong optical absorption are observed. The combinations of structural, electronic, mechanical, and optical properties make α-trigraphyne and twin α-trigraphyne suitable candidates for use in photovoltaics and touchscreen applications.