Power- and energy-efficiency continues to be a primary concern in the design and management of computing systems, through from mobile devices (battery life and temperature) to HPC (electricity bills and temperature). In this talk I will give a summary of our research into the runtime management (RTM) of multi- and many-core computing systems, that have come out of the PRiME (www.prime-project.org) and Graceful research projects. I will present a range of different approaches that we have developed and experimentally validated, and the key findings that we have made along the way. These encompass 1) exploring RTM on both novel and heterogeneous/homogeneous COTS multi-core platforms, 2) the impact of core scaling on RTMs, 3) issues and approaches for managing concurrently executing workloads on shared resource, and 4) comparing the impact of offline vs online characterisation approaches. I will also present a range of open-source tools that we have developed and released through these projects, spanning simulation and runtime power models for multi-core CPUs, to a framework for researchers to incorporate multi-core runtime management into their system and enable level comparison with the SoA.