RetroPaint

RetroPaint is a fun piece of software that enables you to remember the old times when the most popular computers out there were Commodore 64, ZX Spectrum, or Apple II 1977, by allowing you to convert pictures to the colors displayed by those machines' monitors.
The program is sufficiently simple to understand and use, but it only supports BMP format images, meaning that if you wish to work with other types of pictures, you will first need to convert them.
RetroPaint allows you to load the image into the application, then select the filters you want to apply, by moving the sliders left to right and opting for up to three of the several available retro looks, such as 'Commodore Vic-20', 'Atari ST', 'Spec256 Emulator', 'Apple II', 'Sharp MZ', 'MSX Systems', 'ZX Spectrum' or 'Amstrad CPC' or 'Custom Palette'.
In the case of 'Custom Palette', RetroPaint enables you to create a personalized 32-color scheme for any of the options you pick, either by drawing them randomly or by entering each color's RGB values.(You can do this by clicking on the light-blue button.)
Moreover, you can perform a variety of image editing operations, like 'Contrast Priority', 'Dark Color Difference', 'Penalty RGB Equivalents', 'Penalty Saturation', 'Fixed Color Difference', 'Basic Dithering' or ' Light Setting'. You can then press on the 'Start' button and RetroPaint will provide you with a side-by-side view of the converted pictures, with up to three different results. The files can be saved to your PC by pressing the the 'S' button on the screen or on your keyboard. However, the exported picture features the compared view and not each image individually.
To conclude, RetroPaint is an interesting and fun application that allows you to remember how images used to look like on your old computer and compare the different results amongst each other.