Non-Linux FOSS: Scripts in Your Menu Bar!
There are hundreds of applications for OS X that place information in the menu bar. Usually, I can find one that almost does what I want, but not quite. Thankfully I found BitBar, which is an open-source project that allows you to write scripts and have their output refreshed and put on the menu bar.
I personally use it to fetch Bitcoin and Ethereum prices, but because you're limited only by what you can get Bash to output, it's extremely flexible. Even the method by which you change update frequency is elegant. By adding a refresh rate to the name of your script, the program refreshes only as often as you desire. You can see an example of my Bitcoin price-fetching script in the screenshot (Figure 1). Also notice the file format for my additional scripts (Figure 2).
Figure 1. Bitcoin Price-Fetching Script
Figure 2. File Format for Additional Scripts
download the binary or the source code here. There is also a huge library
of user-contributed scripts so you don't have to start from scratch. My
Bitcoin script is actually from this repository, and I based my other
scripts off that. Whether you want to pull text from an API like me or
grep the temperature from a weather page, BitBar is simple and
elegant at the same time.