FNET is a low-cost, GPS-synchronized wide-area power system frequency measurement network. Highly accurate Frequency Disturbance Recorders (FDRs) [...] measure the frequency, phase angle, and voltage of the power signal found at ordinary 120-V electrical outlets. Animated map. [via]
Kropla's World Electric Guide - outlets / power plugs of the world (map), along with an index of international voltages and frequencies for travellers. Plugs in the future: modular, stylish, smart, eco-friendly, rotating, collapsible, or gone entirely.