The early computer era is largely undocumented, and we do know that programmers have been messing around with making games since the home computer was first introduced. Back then, DOS games were the norm, small text adventure games were everywhere.
Firstly, back then it was really exceptional to run software that weren't released by official companies in public shops. There were BBS, but mostly operated by Universities, for their students needs. More important, before the release of the
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(1981), each modem had its own set of instructions, what made them none inter-connectable. And, obviously, at those time you were limited to 1,200 bauds at max, while the smartmodem was only at 300 bauds.
Secondly, back then DOS was an anecdotal Operating System that could hardly run on more than 10% of the computers owned by individual.
Were there a homemade porn game made by someone in his basement and shared with a handful of people? Perhaps. Can it be called "the first porn game"? No, precisely because only a handful of people heard about it and even less could play it.
If I were to place my bets on the first adult game, it would be one of those DOS adventure/role playing games.
Well, I have a good and a bad news for you.
The good news is that Softporn
is a text adventure RPG game that was, among other platform, released for DOS.
The bad news is that, according to your own claim above, the first porn game can
not be a DOS game, since
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(the very first version of DOS) only date from late 1979 and was only available for computer using both a i8086 CPU and an Altair expansion bus. This mean that it could be used on even less computers than its following released as MS-DOS. The most available OS at this time was
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(/!\ the letters are C and P, and must be corrected also in the link), the only one that could run on the most used CPU available at those times.
One that may have not been released to the public, or circulated around groups of friends since the internet likely wasn't really a thing yet and thus was never published online.
Yeah, before 1981, release date of Softporn, "internet likely wasn't really a thing yet", it's the least than can be said. Internet do not existed before the normalization of its
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(TCP and IP) in 1982. This while it's only in 1989 with the
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that Arpanet started to be opened to other clients than institutions.
Furthermore, things become even more blurry when taking into account other countries involvement.
The video game industry in the West, most notably the United States, is pretty well documented, but that's not the same in other countries. Most notably Japan and Russia, who have both played large roles in this community at one point or another.
Among the seven platforms on which Softporn was playable, five as Japaneses ones... But yeah, sure, we don't know much about Japan market at those time, while I have bigger boobs than Lolo Ferrari (and mine are naturals)...
Plus, once again, online sharing wasn't really a thing before early 1980s even in Japan. JUNET, the first network operated in Japan, date from late 1984
[point 4.3] and, while BBS took an important part in Japanese computer culture (with PC-VAN and NIFTY-Serve), they really started late 1980s, partly due to the communication cost, partly due to the difficulties to handle Japanese characters through networking protocols at those times
(something that increased the communication time, and therefore cost, since it couldn't be encoded over 8bits) [point 3] [
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].
Be noted that the communication cost issue do not limits to Japan. For most countries outside of the USA
(and even in the USA for none local communications) it stayed a major issue and main reason why BBS had limited usage before public modems reached 9,600 bauds (32 times faster that the original 300 bauds) what started to make software download affordable; yet it was still ~1KB/second, therefore between a 5 and 10 minutes communication just to download one software.
Still, it's only in the early 1990s, with the first 14,400 bauds modems (1991), that 9,600 bauds ones started to be actually affordable for the public. Reason why, even in the USA, BBS only actually started to rise with the 1990s. Unlike what one can think, it's not the release of the IBM PC, and therefore the first home computer standardization, that led to this, but really the fact that speed started to be bearable.
Any teenager who used BBS, even in the 90s and at 14,400 bauds, can tell you that the cost was really a strong issue, and source of harsh punishment.
TL;DR:
In the real world where we live, even if it existed that "first porn game that isn't softporn" never had more than a handful players, with "handful" being bellow 10, and was running on **/M
(still C and P), if not on a propreritary OS.
Edit: Yeah, obviously, it's not really an OS compliant with the only censoring rule here 
