Existing funding systems fail to sufficiently fund public goods and common goods due to insufficient mechanisms for coordinating various agents towards valuable outcomes. Relative to traditional capital systems that scalably organize activity around maximizing financial performance, impact funding remains underdeveloped, especially in the ability to reward high-upside, high-uncertainty work. Here, we propose Impact Evaluators (IEs) as a modular system for coordinating work by measuring, evaluating, and retrospectively rewarding the impact achieved towards specified valuable objectives. We present a structure to define Impact Evaluators as well as design schematics to facilitate their implementation. We then discuss implementation considerations, practical learnings from past experiments, and integration with the broader ecosystem of public goods and commons funding systems.