Appears to be based on a very similar design to https://news.ycombinator.com/item?id=7882066 , except that batch files are far more limited than bash.

Also, may I suggest a small optimisation to APPFB.COM : there is no need for push cs/pop ds at the beginning, because in a .COM format executable all the segment registers are initially set to the same value. You can eliminate two unnecessary bytes ;-)