ZPE nightly was introduced so that when a change to any version of ZPE was made, the download would automatically be the latest version. Ultimately, nightly was supposed to be the latest, but it was not necessarily the most stable version of ZPE. Alas, the plan to deliver this didn't really work as it relied on my laptop being on.
The good news is that now, ZPE nightly is the most up-to-date commit on my GitHub. Once I commit to GitHub, the nightly will always be the ZPE that's on there. This means you can try out the latest and greatest ZPE anytime. You can head to my Download Center to download the newest version right away.