The 6.1 version of Drainage is provided as a free download on our website. The program relates to Education Tools. The actual developer of the program is Archon Engineering.
From the developer:
This program will allow the Engineers or Contractors to perform a quick estimate of the required drainage facilities for small construction projects.
The program consists of four parts. The first function is the Runoff calculator. The user uses this function to estimate the amount of runoff in the area of concern. From this output the user knows the flow capacity of runoff that he has to deal with.
You may want to check out more software, such as GaticSlotDrain, MWell or Site3D, which might be similar to Drainage.