FastRecorder - is an audio recorder application with advanced and simple features of recording voice memos, on-site sounds and everything around you. The main feature is that FastRecorder supported on Apple Watch and can be called directly from your customized clock face.

Written using Swift language. iOS app include 3D Touch support and widget to make quick audio notes, and ability to crop recorded audio. Apple Watch app support recording audio in background mode.

What they say:

FastRecorder was mentioned as one of the top applications for Apple Watch by MacLife UK