This is a really simple Nth letter frequency plotter. It was created a long time ago for a cryptography problem set for frequency analysis on the Vigenère cipher.
What you'll notice is that the x-axis is the English alphabet ordered by expected frequency, most common first. With this ordering, you expect to see a particular decrease from the leftmost column to the rightmost column.
The plotter itself is incredibly simple — you don't really need it. You can do this easily in Matplotlib or GNUPlot.
I keep this thing around because the bar chart looks nice, an English curve is easy to spot visually, and it reminds me of one of my favorite courses from my school days.