This is definitely not exhaustive
The Environemental System Research Institute (1969), ESRI is the world leader in GIS softwares(Arc info, ArcCAD,Arcview,ArcIMS). The marked is very open. The hydrologists are NOT the main customers since they need ultraprecise data and hudge computations. Different licences leads to expensive recurent costs (15,000 Euro/year for the IMFT university version)
Geographic Ressource Analysis Support System (GRASS) originally developed by the US Army Construction Engineering Researsh Laboratories (USA-CERL) is the new outsider in the GIS market. Users are NASA, NOAA, USDA, USGS, and many scientific groups.Free and well designed for scientific application, as described in the following part.
The conference menu - Getting information - GIS market - Grass anatomy - r.profile function - r.watershed function - Computed waterlines - Screenshots