xnec2c is a GTK+ graphical interactive version of nec2c. It incorporates 
the nec2c core which it uses for reading input files and calculating 
output data, but it does not need and indeed does not produce an output 
file by default. Since xnec2c incorporates the nec2c core, it has access 
to all internal buffers, including structure data, frequency-related 
data (structure currents, input impedance, gain etc) and radiation pattern 
data (for the far field and near field). It therefore has the ability to 
graphically display user-requested data directly, as the frequency loop 
progresses or after input from the user. Graphs of frequency-related data 
and the current or charge distribution evolve as the frequency loop 
progresses, and radiation patterns (far and near field) are sequentially 
drawn for each frequency step. A new frequency can be entered by the user 
from spin buttons in the main or radiation pattern windows or by clicking 
on the graphs of frequency-related data. New output data are then computed 
and displayed in text and graphical form.

nec2c is a C translation of the Fortran nec2 code, which allows analysis
of antennas.