A Calculator for Confidence Intervals
  A calculator program has been written to give confidence intervals on branching ratios for rare decay modes (or similar quantities) calculated from the number of events observed, the acceptance factor, the background estimate and the associated errors. Results from different experiments (or different channels from the same experiment) can be combined. The calculator is available in http://www.slac.stanford.edu/~barlow/limits.html 
Roger Barlow