IrfanView is a popular and versatile image viewing, editing, and converting software application. It is available for Windows, Mac OS, and Linux operating systems. It can open a wide variety of image file formats, including JPG, BMP, PNG, TIFF, and GIF, as well as some audio and video formats. It supports basic image editing functions such as cropping, resizing, and rotating, as well as more advanced editing options such as adding text and shapes, color correction, and applying filters. It can also be used to batch-edit multiple images at once. In addition to its image editing capabilities, IrfanView can also be used to create slideshows, capture screenshots, and convert files between different image formats. It also includes a built-in media player, allowing users to view audio and video files. IrfanView is free for personal use, and can be extended with a variety of plugins to expand its functionality.
XnView has dozens of tools and filters for quick image editing, as well as an integrated file manager with various functions for organizing images. Plus it all works on both Windows and Linux. It's a bit slow compared to Irfanview, but it's still one of the best programs of its kind.