Gravity

Specifically designed for Paint.net, Gravity is a plugin that enables you to make an object look like it's pulled down by gravity. It does so by making pixels move downward from transparent pixels placed above it. The motion is interrupted as soon as it meets opaque pixels.
Although the tool might seem difficult to work with, it can be handled not only by users experienced with this particular image editing application, but also by beginners.

How to set up and access

Setting it up is simple, since all you have to do is copy the downloaded DLL file to the "Effects" folder of Paint.net's installed directory. It can be similarly integrated with a portable edition of the program.
If it's already running, you need to restart Paint.net to finalize the setup and make room for the new extension. It can be found in the "Effects" menu.

Apply a gravity effects and configure settings

The main window gives you an overview of all options in a neatly organized structure. Apart from selecting the gravity's direction (left, right, up, down, null), it's possible to replace the matching colors with transparent pixels, as well as to adjust the green, blue and alpha channels by moving sliders or entering numerical values. Any of these four settings can be restored to default with one click.
Furthermore, you can disable any channels by entering -1, equalize the red, green and blue levels (the red slider), as well as reverse the test. Worth noting is that photo effects can be previewed while making them. This way, you don't have to apply modifications, check results, and undo actions or remove the newly created layer if you change your mind.

Conclusion

It integrated with the latest edition of Paint.net smoothly in our tests, although it hasn't received updates for a long time. Gravity didn't causing the image editor to hang, crash or display errors.