mezoGIS is a GIS application, a graphical interface to query and analyse spatial data. mezoGIS does not store or compute data directly, but operates external PostGIS databases. The goal of mezoGIS is to provide a tool for geo-spatial analysis with PostGIS, through on-the-fly SQL queries as well as through larger, external plugin scripts.
There are other, excellent open source applications that can display PostGIS data sets (like QGis or GRASS). Those projects, however, expect properly indexed tables as an input, and don't provide a built in functionality to launch SQL queries. The focus of mezoGIS is to stay close to the SQL workflow: Spatial queries are launched through manually entered SQL commands, and result sets containing geometry are displayed as map layers.