[michaericalribo]

R itself was first released in 1993, and is based on S / S-Plus which date to the 70s...moreover, these have been standard tools since the 80s at least, well before Gretl...

[nerdponx]

R was considered "just a stats package" until the last 10-15 years.

[goosedragons]

The S of the 70s and 80s was a different beast. It was more macro based like SAS. R really didn't start to gain traction until the 2000s.