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The current, stable version is known simply as "ImageJ"—or sometimes "ImageJ1" or "IJ1" to differentiate it from ImageJ 2.x, which is still in beta. Read more...

ImageJ2 ImageJ 2.0.0, referred to as "ImageJ2" or "IJ2" for short, is currently in development. It is a complete rewrite of ImageJ, but includes ImageJ1 with a compatibility layer, so that old-style plugins and macros can run the same as in IJ1. Read more...

Fiji Fiji is a distribution of ImageJ (both ImageJ1 and ImageJ2!) for the life sciences. It provides a large number of additional plugins to facilitate analysis of life sciences images, particularly microscopy images. Read more...

Or see the table of ImageJ flavors for a more complete rundown of various ImageJ-related software.