The rapid progress of nanophotonics demands theoretical frameworks capable of predicting the resonant behavior of complex systems comprising constituents of varying nature, operating beyond the weak-coupling, high-Q regime where classical temporal coupled-mode theory (CMT) is applicable. This work presents a coupled-quasinormal-mode (cQNM) framework for analyzing dissipative coupling with photonic and plasmonic resonators. The framework provides rigorous closed-form expressions for nonconservative coupling coefficients and introduces novel features, such as a new coupling scheme via time derivatives of excitation coefficients. It delivers transparent and accurate predictions of exotic phenomena—such as zero-coupling between very close cavities and level-attraction effects—that are only vaguely captured by traditional CMT models. Efficient and user-friendly, this framework facilitates rapid parameter space exploration for device design and offers potential for extension to nonlinear and quantum systems in future applications.