@TheForArkLD recommended that I make a pi approximation in Fortran, so here it is! This is specifically Fortran 90. This is one of my multiple pi approximations in various languages.
Here are the other approximations:
APL - https://repl.it/talk/share/p-in-APL/34888
Forth - https://repl.it/talk/share/p-in-Forth/34652
LOLCODE - https://repl.it/talk/share/p-in-LOLCODE/34421
Python and Node.js (Node is linked in post) - https://repl.it/talk/share/2-Approximations-of-p-In-Only-Four-Lines-of-Code/32773
C - https://repl.it/talk/share/p-Approximations-in-C/33461
I'm also thinking about doing BASIC soon since I've already made Pong and Snake in it and have a good idea on the language now.
Credit to @TheForArkLD , @Warhawk947 , and @LizFoster for inspiring these approximations. Most of these use the Nilakantha Series, although I also use the arctangent method (multiplying the radian arctangent of 1 by 4 to get pi and getting the arctangent with an infinite series) in three of them (Python, Node, and C).