Traditional physical design flows force users to intermix distinct information relating to logical design, physical design, technology, and tool concerns during chip implementation, leading to high design effort, costs, and time-to-market. We introduce Hammer, a physical design generator which remedies these problems via separation of concerns. Through its modular software architecture, Hammer is able to separate tool and technology concerns, while Hammer's data format separates logical and physical design concerns, enabling physical design information to be generated in sync with changes to the logical design. We evaluate Hammer's flexibility and effective software architecture by demonstrating wide-ranging reductions in time, cost, and design effort in various physical design tasks through multiple tapeouts using multiple technologies (ranging from 45nm to 16nm), tools, and design architectures.