That's Kermit in its very basic version, which is slow but has the advantage of working just about everywhere under extreme constraints. If you have an urge to send data from your C-64 or Tandy CoCo to a Burroughs B5500, there is or was probably a version of Kermit for each that would let you do it. Later Kermits had large packets, sliding windows, and ways to specify what characters needed special encoding.