I just want to remind everyone of my ongoing love affair with Menubar Countdown.
Since 2009 this rudimentary, no-frills timer has been anchored on my menubar. There's a very specific way I use it: It serves as my Pomodoro Timer, which is the only way I get ANYTHING done. It’s running as I type this post. This particular version is free, and only for Mac. Not a Mac user? Just google “menubar timer” for similar options.