Update 1: Three more applications were added to the list, Tux Paint, Pinta and GrafX2.
Update 2: If you are interested in full-fledged, powerful image manipulation tools, have a look at GIMP, Krita (on Steam too) and PaintSupreme. For photo albums and collections have a look at digiKam, Fotoxx or Shutter.
Kolourpaint
Kolourpaint is a feature-rich painting program for KDE with a typical user-friendly interface, supporting many image formats (including PNG, JPG, TGA, PNM, GIF, BMP, XPM or TIFF). It allows zooming in/out, copy/paste, printing, cropping, rotating, applying various effects (balance, emboss, soften & sharpen). I think it is a perfect application for making simple paintings or sketches.
MyPaint
MyPaint offers many features and also an interface which is somewhat unusual among painting applications. There is the actual workspace and a separate window with predefined brushes to select from. It features usual functions, including undo/redo, zooming in/out, many brush types, several effects. Two noteworthy things to mention here are the existence of layers and also the brush editor, which allows you to create your own brushes.
mtPaint
This application is full-fledged, and comes by default with a black background. It offers application-specific settings (like showing/hiding toolbars, splitting window), and also various effects, channels, or layers. Although it’s pretty good and has many options, I doubt it’s a good match for kids.
Gnome-paint
This is a very simple drawing application for the GNOME desktop with a typical interface and few options. It offers basic functions and two sidebars: one to choose the tool to use and the other one to choose the color. The feature to insert text is not yet implemented.
Gpaint
Gpaint is yet another simple painting program from GNU, built with GTK, which offers standard functions and quite a few effects, like sharpen, emboss, oil paint or solarize. There is no undo function.
Tkpaint
Tkpaint is written in Tcl/Tk and offers predefined shapes, various line types, text inserting support and several other tools. It can open GIF, PPM or BMP formats and will save the output image as Encapsulated PostScript or Tcl script.
XPaint
XPaint is rather a nice painting application, including a C script editor, toolbox, brush selector, font selector, color and pattern editor, and even a magnifier.
Addition: Tux Paint
Tux Paint is especially designed for kids, and it provides bulleted buttons for the usual painting tools and brushes. The very nice thing about Tux Paint is that it provides various sounds when the paint tools are used or selected.
Pinta
Pinta is yet another powerful application for GNOME, featuring zoom in/out, fullscreen mode, rotate, resize, brightness/contrast and hue/saturation settings, brushes and the typical painting tools. Except for those, Pinta also offers various effects and layers.
GrafX2
Finally, there is GrafX2, which is a bitmap painting program for X, specialized in 256-color drawing. It is not suitable for children since it is a per-pixel drawing program and the interface may be a bit hard to get a handle on at first.
Rassam-paint
Rassam-paint is a simple painting program written using GTK2 with basic tools such as pencil, brush or flood fill, shapes (line, rectangle, ellipse) and support for all the popular formats out there (PNG, JPG, TIFF, ICO etc).
Install Rassam-paint 1.1 in Ubuntu 14.04, Ubuntu 14.10 and Mint 17
DEB packages are available for both 32-bit and 64-bit systems, as well as pre-compiled binaries. To install Rassam-paint in Ubuntu or Mint you can download the DEB file for your architecture (32-bit or 64-bit) and either double click it or open a terminal and type the command below:
For 64-bit, download the DEB from here and to install it type:
sudo dpkg -i rassam-paint_1.0_amd64.deb
For 32-bit, download the DEB from here and to install it type:
sudo dpkg -i rassam-paint_1.0_i386.deb
The program will be installed as /usr/bin/rassam-paint.
The alternative would be to download the archive which contains the pre-compiled binary, then uncompress it, then run the program. The archive is decompressed in the current directory unless specified otherwise, with no root directory. The unzip package will need to be installed as well (sudo apt-get install unzip).
For 64-bit download the archive from here and type in a terminal:
unzip Rassam-paint_64bit_1.0.zip ./rassam-paint
For 32-bit download the archive from here and type in a terminal:
unzip Rassam-paint_32bit_1.0.zip ./rassam-paint
Hema 