Pixi Paint

Pixi Paint is a small, but fun piece of software that provides you with a basic set of tools so that you can design icons for applications and other utilities you are developing.

Comes with a rugged, yet intuitive and organized GUI

The setup is simple and straightforward, as it solely entails decompressing the archive and you can start using the app right away. The tiny program comes with an unpolished, yet user-friendly and well-structured interface. While most of the UI is dedicated to the drawing area, you have several utensils around it, such as the palette, the drawing tools and a toolbar located in the lower region.
You should know that the application allows you to export your work to PNG only and that you can work on a single project at a time. It would have been nice if the utility supported more file formats and multiple tabs, so that you can multitask when you are working on similar icons, for example.

Includes only a handful of drawing utensils

The application is as simple as it looks and comes with very basic tools, namely a brush, pencil, line tool and two shapes, rectangle and circle. On the plus side, the utility enables you to draw in symmetry mode, toggle the grid on or off and load a new palette. In addition, you have unlimited undo and an adjustable zoom so that you can analyze possible errors efficiently.
As a side note, the colors available can be modified by replacing their HTML color codes, a feature that opens up a world of possibilities in terms of the hues you can employ. It would have been useful if the app included a tool that allowed you to get the color code of the pixel, so you do not have to employ other third party software solutions.

A handy utility for creating icons

In the eventuality that you are just learning the ropes with application development and you are looking for an easy-to-use tool to help you design the icons for them, then perhaps Pixi Paint might be worth a try.