MSDViewer (My Schematic Drawer and Viewer) is a schema editor using a simple text file as input. Requires tcl/tk (>8.4) and Iwidgets (>4). should work on every platform supported by tcl/tk. Output postscripts.
CAVOR is an engine for building apps that involve both graphic and text/numeric data. Primarily GIS is the initial focus, but consider also CAD, CASE, project management (eg PERT charts), and others. Built-in scripting, C API, also supports Tcl and Java.