Geospatial Modeling Environment (GME) grew out of Hawth’s Tools, a collection of tools that provided welcome and easy functionality with an ArcGIS-interoperable toolbar. It has always been optimal for environmental and ecological work, but its functionality can be applied to many other application areas. Now a stand-along package, with all of the original bits and more. It has software dependencies on both ArcGIS and R; see the download page for more information.
IDRISI, a long-standing product of Clark Labs, integrates traditional GIS functionality – focusing on raster-based analyses – with additional digital image processing opportunities. Their application areas are particular strong in natural resource management, environmental modeling, and related land planning and analysis. Their use in GIS classrooms is not as widespread as other platforms, but loyal customers abound.
P.S. IDRISI is not an acronym, but rather a tribute to Muhammad al-Idrisi, the 12th century Islamic geographer and cartographer.