That being said, I could easily add a feature to record any other input device on the system, and then you can install the Soundflower kernel extension (or one of Rogue Amoeba's other excellent utilities) to create a loopback audio input device.
I always watch short video game replays with the audio off or on gfycat or whatever where there is no audio anyway, and for capturing bug reports or whatever I don't need audio either, so I didn't feel like I was missing much without audio for myself.
All that said, if the CoreAudio team would come to their senses and provide a userland API for doing system audio capture, I would definitely be on that.
https://itunes.apple.com/us/app/monosnap-screenshot-editor/i...
i used to use annotate but it got abandoned when dropbox updates their api so i switched to monosnap since.
I've got ScreenFlow on Cmd-Shift-2 and now RetroClip on Cmd-Shift-5!