Paint.NET is one of the best image editing applications for Windows and it has a version for Linux too, called Paint.Mono (or Mono Paint). According to Miguel de Icaza, most of the features in Paint.NET have been ported over to Paint-Mono, with more to come. Apparently, this should also work on Mac OSX, details HERE.

gnome-paint is a simple, easy to use paint program for GNOME. It is inspired on MS-Paint.

paint-mono is a port of Paint.NET. The only way it could be built in the past was using a development version of MonoDevelop and there was no way of generating packages for it.

Gimp Paint Studio is a package of new tools and additions which provide improved capabilities focused on drawing and painting for Gimp.
To install Gimp Paint Studio it, first we must know where the user directory of Gimp is located. Assuming you have installed version 2.6 is usually found at:

If you use Linux, have a tablet (or a pen/tablet addon), and want a graphics tool designed specifically for that device, you need to take a look at My Paint.

Novell open source programmer Jonathan Pobst has released version 0.2 of his simple Pinta painting application for Gtk modelled after Paint.NET, adding a number of new features, including 5 new tools, 5 new adjustments and 5 new effects

Pinta is a drawing/editing program modeled after Paint.NET. Its goal is to provide a simplified alternative to GIMP for casual users. It currently supports most basic drawing tools, unlimited layers, unlimited undo history, and a wide array of image adjustments and effects.

We are pleased to announce the winners of the 2011 Tux Paint Summer Contest. We thank all the participants for thier entries. We must admit, judging was extremely difficult so we decided to add an additional 10 winners who will each get a Tux Paint t-shirt.

Grab Tux Paint, make a cool drawing, win one of 3 OLPC laptops, one of 10 Sugar-on-a-stick and other awesome prizes! The 2011 Tux Paint Summer Drawing Contest is sponsored by Worldlabel.com and is open to all children aged 3 to 12 who live anywhere in the World!