At work on my windows machine I've used Autohotkey to remap the CapsLock key to ESC. I've gotten used to it and on my personal machines (mac) I keep hitting CapsLock out of habit when I want ESC.
How do I do the mapping on the Mac? The keyboard & mouse prefpane has some basic options for the capslock key, but that only lets me reassign it to ctrl, command, or option.
My friend pointed me to something that worked. He said to install both PCKeyboardHack and KeyRemap4MacBook. PCKeyboardHack allows for remapping capslock, while the other one seems to allow for a lot more remapping. I'm not sure if both are actually required (you might be able to use just PCKeyboardHack), but I installed both just to play with them. Seems to be working well for me.
Since macOS 10.12.1 it is possible to remap Caps Lock to Esc natively (System Preferences -> Keyboard -> Modifier Keys).
You can try DoubleCommand. I haven't personally used it but based on a screenshot there's an option to remap the Caps Lock key to ctrl. You may be able to change that to Esc.
In response to your question, I just put out a new version of Consistent Keyboards that can do this. It's a undocumented feature, however, and requires a manual step to turn on, as follows.
After installing version 0.7, edit the file /Library/Application Support/Ljosa/Consistent Keyboards/config.plist. Change the value of x-caps-lock-is-esc from false to true. Finally, do sudo launchctl stop com.ljosa.consistent-keyboards to restart the program with the new settings.
