Round Robin Database Tool
This powerful database/graphing tool comes with bindings to Tcl:
load tclrrd.so Rrd::create ...
See http://oss.oetiker.ch/rrdtool/ (URL updated by MAKR - 2007-06-19)
Designed to represent time series data, often used by ISPs to visualize network-traffic through routers etc.
The Tcl bindings are part of the RRDTool sources (see bindings/tcl subdirectory).