What exactly makes you think it’s a word when it’s clearly an initialism? Do you also write MS-DOS as "Ms-dos" or BBC as "Bbc"? (Or NATO as "Nato", though that one actually has better grounds to be written like that, being an acronym rather than an initialism – in some orthographies acronyms are indeed written like proper nouns.)
When it's written in all lowercase, like in the title, that's a stylistic preference that you can disapprove of if you want, although it's an incredibly petty thing to care about.
> Yes.
Well, that's your prerogative, but it's against standard English orthography. Acronyms and initialisms that refer to proper nouns are spelled all uppercase in English. FBI, NASA, WHO, GCC, HSV, NY, no "Fbi", "Nasa", "Who", "Gcc", "Hsv", or "Ny". You'd never get the latter versions past any remotely competent copy editor or grade school teacher.
As an example of different orthography, in standard Finnish NASA would indeed be spelled "Nasa", but FBI is still FBI and DJGPP is still DJGPP.
An acronym. The "GPP" is the DOS-ified spelling of "g++"; the '+' was not (officially) allowed in MS-DOS filenames. The DJ stands for the first name (not the initials, apparently [1]) of the project's originator, DJ Delorie.
Although: "Since C++ is integral to gcc, djgpp no longer stands for "DJ's G++" but probably stands for something like "DJ's GNU Programming Platform"." [2]
DOS:
"One of our commands allows separation of filenames with a + symbol, so we need to prohibit that character."
"Couldn't we rework that command to not use + separators?"
"No, far better to take that character out of consideration."
Unix:
"Filenames can use control characters. I don't care if that makes pipes between commands really complicated! Add an option for NUL-separated filenames if you have to."
Additionally, word-initial single G before short I is always [g] instead of [dʒ] in native English: gift girl give gibbon gimlet gizzard gilded git gimp giddy gig gimbal.
The exceptions are
borrowed French words: gin (le gin), ginger (le gingembre), giraffe (la girafe), giblet (OF: gibelet).
I personally follow the "I am the user, my rules" when it comes to language rules :P. It is at least as strong as "their word, their rules".
Also I can see that Paul Graham's "my website my rules" is even stronger than mine or DJ Delorie's, so Djgpp is also correct (if not by the Gods, then by fist).
The linked site starts sentences with "djgpp 1.05" and "djgpp 1.06", so maybe the software name has a different irregular capitalization than version names, which stay lowercase no matter what.