I've been stewing on this for close to two years now, but I have a surprising ally in my slow-burning quest to eventually start some archaic old-world gaming set in as close to a historical setting as I can possibly manage, with the first planned campaign arc to take place in ancient Egypt. That ally would be my son! He became quite interested in Egypt after playing Assassin's Creed: Origins which, despite being a single player game, he and I played borderline competitively just to see who could level up the fastest and do the most quests. Say what you will about video games, but the level of authenticity that Ubisoft put into trying to make a fun but also reasonably informative historical setting out of late Ptolemaic Egypt really caught my son's attention, and he has proceeded to move beyond just the game, reading books and pursuing questions. We even let him play in our ongoing Call of Cthulhu Delta Green campaign not long ago, in which he played an expat marine named Bayek who had retired from the rough life in Cairo, and who secretly heard voices in his head from Anubis.
This is a short way of saying that I see two opportunities here: one is to spring an Egypt campaign on my group that is legitimately aimed at close historical authenticity (but likely at times with supernatural elements because those are always fun), with at least one player (Marcus) as an advocate. The secondary opportunity is it lets me run historical games which can (hah! surprise!) impart more history lessons disguised as actual good old fun. Sneaky!
The trick is determining what game system to use. I have a number of systems which could get the job done, but with the caveat that the system needs to skew close to realism as a baseline (so supernatural elements may exist, but the characters are going to have the veneer of historical verisimilitude as the goal). Want to play an Egyptian warrior loyal to his Pharaoh who thwarts assassination attempts while secretly believing he communes with Anubis or Sobek in his dreams? Sure! Want to play Anubis, or a Set-beast or something weird like that? Nope, not the goal here.
The best book I have found so far, outside of simply doing my own research, is GURPS Egypt. It's got that "surprising amount of information packed into a short book" GURPS quality that was so amazing with GURPS 3rd edition era resources from the 90's. It's only downside is its statted for 3rd ediiton, which is no big deal for a GURPS Fan to translate to 4th edition, but a bit of a headache explaining to GURPS noobs. Indeed, the single biggest hurtle I can see if that I think a lot of players feel GURPS is a tough system to master not because of its complexity (it's really not that complex) but because of its freedom of choice in design....the decision paralysis can be thick.
So some alternatives include the BRP family of games, including but not limited to Call of Cthulhu 7E with the archaic era guidelines turned on; the BRP Gold Book; the Mythras rules (arguably quite suited to this, but requiring me to think hard about the combat system which I have issues with) and Open Quest 3, which I am leaning towards right now. I am evaluating how easy it would be to modify OQ3 to work.
Of the BRP games above, I'd probably eliminate Mythras (the combat is too simulationist for the group I am aiming at). It does have a great module (Temple of Set) which could be adapted to an Egyptian setting, maybe.
BRP could work fine, but Open Quest 3 is a more streamlined and easier to use edition of the system, and I've been itching for an excuse to use it anyway. But if I went with a period-set Call of Cthulhu (maybe sans Cthulhu stuff, maybe not) I know that everyone would handle that variation of the system just fine.
Other systems include True20, which recently returned to print as a POD product. I like it, but the key issue is (similar to GURPS) getting buy-in and then getting everyone up to speed. It's not really that complex a system, either, and may be an easier sell. Does it have enough support material to make adapting it to a quasi-historical Egyptian setting work? I think so.
Cypher System is a fine generic system but its also inherently suited to gonzo/creative endeavors. Yes, historical setting are discussed in Cypher, but I think it would be doing the system a disservice to run something aiming for a baseline of realistic and low-key with an emphasis on historical accuracy. If I were going to run something in which everyone, for a random example, played actual Egyptian demigods or something then I think Cypher would be extremely well suited to such a game. Maybe in the near future!
I thought about D&D/Pathfinder for a bit. Unfortunately the current iterations of both Pathfinder and D&D are really hardwired to the D&Disms of their default/implied settings, so the result would be "D&D or Pathfinder, but with a shiny veneer of Egypt." I've technically been running that for two years now with Pathfinder at least in my Egyptian/Roman Republic inspired Oman'Hakat campaign. D&D style changes the feel, and as a good example of the extremes one might go through just to make it work I would showcase the old Historical Reference books TSR published for AD&D back in the day, or the many third party products that came out for D&D 3.5.
Indeed, there are several Egyptian sourcebooks for D&D (and both Pathfinder and Castles & Crusades) out there, but all of them are distinctly "D&D fantasy, with Egyptian style" rather than more authentic historical treatments. That said, these tomes might have some useful content. Codex Egyptium for C&C has an interesting take on Egypt, and is mostly aimed at a historical representation laden with a heavy treatise on many, many gods. That alone is useful, though I wish the book provided a bibliography of the resources used by the author, which makes it difficult for me to do more research and reconcile variances in this book with other research I have done.
Likewise, the two main Egyptian themed books I have access to that bear mentioning is Necromancer Games' Necropolis (the 3.5 edition; the 5E Kickstarted edition appears to be in shipping hell right now); and the Hamunaptra boxed set from Green Ronin. Both are decidedly "D&D fantasy, now with more Egyptian stuff"...think "Like going to Egypt, but you visit the Luxor Casino instead" type stuff, but the actual adventures and content can be mined for some ideas.
The best overall resource remains GURPS Egypt, though, along with GURPS Places of Mystery and GURPS Low-Tech. Those are likely the only three game-related books I need at the table along with my library of actual books of Egyptian Archaeology, magic and warfare.
So....for the moment, I think I have to decide on using Open Quest 3, True20, or GURPS as the best overall choices. I think if I take some time to prep the 3rd edition GURPS content for 4th edition templates it will help, a lot. But...Open Quest 3 looks to provide a sound experience, and is easily quite familiar to the group. True20 less so, but I think once people see how it works and how character generation flows it will prove quite easy.
The big decider will probably be, "which of these games have the best character sheet setup in Roll20" though. I guess I should look there first!
UPDATE: Roll20 has GURPS character sheet, which looks overly complete and scary, especially for largely new players. If I go that route, I may need to make an opening game that is a shorter introduction and do some pregens. True20 has representation, which is good. Open Quest 3, much to my disappointment, does not have a character sheet on Roll20, though.
Despite what I said above, I may peruse the "historical" stuff in Cypher a bit more, and think about it. I should not dismiss Cypher out of hand just because the goal is "historical realism." Stay tuned....
