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

You can 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 possibly grep the temperature from a weather page, BitBar is simple and elegant at the same time.