There is a new version of the Gentle Introduction to Category Theory. There are no new chapters this time, but there are some significant additions (I now prove a result about Cartesian closed categories with natural numbers objects, which previously was only announced, and prove that free monoids can be thought of as initial objects in a certain comma category). And there are many improvements, both in content and presentation. Note in particular, I correct a mistake about the relation between different notions of diagrams, and clear up what was an unnecessarily messy chapter on the existence of limits. I am very grateful indeed to comments/corrections from Paolo G. Giarrusso and Yufei Cai for prompting some of these improvements.
Although now 178pp., this version is still very incomplete: you can find some rough-and-ready follow-up chapters at the categories page here where there is also an alternative link to the Gentle Intro for those without an academia.edu login.