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.