AKVIS NatureArt is one-of-a-kind image editor, as it's created with a strict purpose: to let you edit photos that depict outdoor landscapes by adding natural phonemena to them. In other words, this surprisingly cool tool is capable of making pictures look like they were taken during heavy rain, thunderstorm, or really sunny days. The other available effects let you add rainbows or clouds to the photos, or less common phenomena like lightnings, aurora, or frost.
This neat app lets you apply the unique weather effects to your existing pictures, or create new photos, with new nature scenes, from scratch. Furthermore, the available effects, though they're not very numerous, can be customized further, letting you adjust parameters intensity, transparency, and so on, for each one of them. There are also ready-to-use presets that make photo editing using this tool even simpler and faster.
I also like about this tool the fact that it can be used either as a standalone application or as a plugin for apps like Adobe Photoshop, Corel PaintShop Pro, etc. Furthermore, it comes in multiple editions (Home, Deluxe, Business), each with its own set of available features. Last but not least, this program supports all the popular image formats, including the likes of TIFF, JPEG, BMP, PNG, PSD, etc.
To conclude, AKVIS NatureArt is an interesting tool, though a bit pricey considering the rather low number of supported effects.