"Paintbrush for Mac" is a freeware Ms Paint clone.
iPhoto is a stronger image editor from Apple itself and since 2011 it's standard installed on new Macs as part of the iLife bundle.
Will be replaced by "Photos" somewhere in 2015. It's a new image editor that will replace in "free" mode Apple iPhoto and with payable extensions it will replace Apple Aperture
Pixelmator is a very good semi-pro image editor and not that expensive, also there's an pixelmator app for iOS (iPad)
Adobe Photoshop is the go-to app for professional image editor and also has a matching price tag.
So I hope that the above is to your liking with 4 different classes of image editors.