The initial set of programs was created around 1997 by Ignacy Misztal to
Details on programming and computing algorithms are available in an Interbull paper by Ignacy Misztal Complex Models, More Data: Simpler Programming?
Features of Fortran 90 enabled a dramatic reduction in complexity compared to earlier versions of Fortran. Additional simplifications were achieved by putting less emphasis on low-level computational efficiency.
Over time, more and more programming was done by many people (see here), especially Shogo Tsuruta, Ignacio Aguilar, Yutaka Masuda, and lately, Matias Bermann.