Very easy to use gimpshop.mirror
GIMP is good enough itself. This project... I don't see where it's similar to photoshop... For PS users look&feel are the most important things. They could even fail to notice some missing features.
The product has been discontinued because the person who owns the domain name gimpshop[dot]com is a jerk. And I quote the actual developer, "It has been five years, the software has stagnated (due in no small part to my becoming discouraged by this one profiteer who trumped me, stole much of my traffic and bumped my site down to the second result when you search for "Gimpshop"). I assumed the guy would just give it up as I sadly let the project stagnate, but that hasn't happened. In a March 2014 discussion, Moschella states: I originally created Gimpshop, but I'm not the jerk who owns that domain and added adware & spyware to the source. Sorry about that. I hate that this guy is out there making my fun little project into an abomination."