NextishClock 1.0 for Mac was available as a free download on our application library. The actual developer of this free software for Mac is Peter MacWhinnie. The software lies within Theming Tools, more precisely Multiple Desktops.
From the developer:
NextishClock is an alternative to Apple's Window Clock, it has a few extra features such as themes and a calendar. It has both digital and analog clocks built in, so no matter witch you choose, chances are you'll get what you like.
You may want to check out more software for Mac, such as Occurrence Selector, which might be similar to NextishClock.