V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

GSL
       Graphics Software Labs (AT&T)


The Free On-line Dictionary of Computing (30 December 2018):

GSL

   Grenoble System Language.  M. Berthaud, IBM, Grenoble.  "GSL
   Language Reference Manual", M. Berthaud et al, March 1973.  "A
   MOL-Based Software Construction System", M. Berthaud et al, in
   Machine Oriented Higher Level Languages, W. van der Poel, N-H
   1974, pp.151-157.