ruby -e "i=0;loop{puts ' '*(29*(Math.sin(i)/2+1))+'|'*(29*(Math.cos(i)/2+1)); i+=0.1}" #ruby

about 23 hours ago via web

ruby -rtk -e "w=TkCanvas.new(TkRoot.new{title:paint});w.pack.bind('B1-Motion',proc{|x,y|TkcOval.new(w,x,y,x+4,y+4)},'%x %y').mainloop" #ruby

about 3 hours ago via web

Almost got this one short enough to tweet:

ruby -rtk -e"v,w=0,0;a=[1]*9;c=TkCanvas.new;c.pack.bind('Motion',proc{|x,y|a<<TkcLine.new(c,v,w,v=x,w=y,:arrow=>'last');a.shift.delete rescue 1},'%x %y').mainloop"