As the headline alludes to, the biggest change from YOURLS 1.4.3 to 1.5 is the addition of plugins. Now, instead of being forced to modify the core files to change the functionality of YOURLS, users can simply add/install plugins to change the tool’s behavior.
For example, since first installing YOURLS, I’ve wanted it to generate random alphanumeric URLs in the same fashion as bit.ly and other well know shorteners. Until 1.5, I would have been forced to edit the original YOURLS files, which would then be overwritten each time the tool was updated. Now, I simply followed these instructions and got random, 6-character generic short links (e.g., http://jhk.co/3ugduy) within a matter of minutes.
Another notable new feature is the addition of an instant bookmark: “The Instant Bookmarklets will pop the short URL without leaving the page you are viewing.” For more on the rest of the updates and improvements found in 1.5, check out the official changelog.
All in all, v1.5 has made a great tool even better.