decida is used for electron device characterization, procedural circuit simulation and analysis of electronic circuits, or more general data analysis tasks.

From the README:

  decida provides procedures for data visualization:
    X-Y plots, histograms, eye-diagrams, oscilloscope plots,
    smith-chart plots, pole-zero plots

  decida provides procedures for data and signal analysis:
    Fourier and inverse-Fourier Transforms, jitter analysis,
    delay analysis, table interpolation

  decida provides several general-purpose optimizers

  decida is used to build parameter extractors for electron devices such as
  MOS transistors and integrated resistors.  decida provides several optimizers
  which are used to fit device models to measured or simulated device data.
  The parameter extractors use the built-in decida parameter, model, data,
  and extractor objects to configure the extraction process.

  decida is a Tcl/Tk scripting engine which can drive circuit simulations
  in Celerity, HSpice, Spectre, Nanosim and other circuit simulators.
  Procedural simulation and post-processing greatly improves the efficiency of
  many circuit design tasks, such as: simulating process/voltage/temperature
  case-combinations, initial module design involving changes to component
  values, final design verification with post-layout netlist, post-processing
  intermediate and final simulation results, and circuit optimization.