As you might expect, Joulemeter only works on Windows. Joulemeter is advertised as “a software tool that estimates the power consumption of your computer.” Estimates for the power usage of individual components (CPU/monitor/disk/”base”) are provided while you’re running the tool. (No, I’m not sure what “base” is, either. Perhaps things like wifi?) A calibration step is required for trying to measure anything. I’m not entirely sure what the calibration step does, but since you’re required to be running on battery, I presume that it somehow obtains statistics about how your battery drains, and then apportions power drain between the individual components. Desktop computers can use a WattsUp power meter in lieu of running off battery. Statistics about individual apps are also obtainable, though only power draw based on CPU usage is measured (estimated). CSV logfiles can be captured for later analysis, taking samples every second or so.
Power Gadget is cross-platform, and despite some dire comments on the download page above, I’ve had no trouble running it on Windows 7 and OS X Yosemite (though I do have older CPUs in both of those machines). It works by sampling energy counters maintained by the processor itself to estimate energy usage. As a side benefit, it also keeps track of the frequency and temperature of your CPU. While the default mode of operation is to draw pretty graphs detailing this information in a window, Power Gadget can also log detailed statistics to a CSV file of your choice, taking samples every ~100ms. The CSV file also logs the power consumption of all “packages” (i.e. CPU sockets) on your system.
I like Power Gadget more than Joulemeter: Power Gadget is cross-platform, captures more detailed statistics, and seems a little more straightforward in explaining how power usage is measured.
Roberto Vitillo and Joel Maher wrote a tool called energia that compares energy usage between different browsers on pre-selected sets of pages; Power Gadget is one of the tools that can be used for gathering energy statistics. I think this sort of tool is the primary use case of Power Gadget in diagnosing power problems: it helps you see whether you might be using too much power, but it doesn’t provide insight into why you’re using that power. Taking logs along with running a sampling-based stack profiler and then attempting to correlate the two might assist in providing insight, but it’s not obvious to me that stacks of where you’re spending CPU time are necessarily correlated with power usage. One might have turned on discrete graphics in a laptop, or high-resolution timers on Windows, for instance, but that wouldn’t necessarily be reflected in a CPU profile. Perhaps sampling something different (if that’s possible) would correlate better.