GeoTop 1.7 was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. The software is included in Photo & Graphics Tools. We recommend checking the downloaded files with any free antivirus. The actual developer of the free software is Riccardo Rigon.
From the developer:
GEOtop is a distrubuted Hydrological Model which has been developing by Riccardo Rigon and its team since the late 1990s.The original community however is seeking for creating around GEOtop a ecosystem of co-developers and users. In fact from the beginning GEOtop was designed to become a community model, and eventually flowing into major community efforts as the CUAHSI Chymp project.
You may want to check out more software, such as MapSys or TopoSys, which might be related to GeoTop.