Void Pyramid is a brilliant, retro style computer RPG that meshes two very disparate genres, Egyptian mythology and science fiction, to create a really unique setting. The evocative and imaginative descriptions, the elegant and fast mechanics, and the rad soundtrack create a game that explores and combines both of its inspirations very well. I would definitely recommend the game and it can be downloaded for free from the link at the bottom of this post.
The use of both Egyptian mythology and science fiction creates a blend that ignites the imagination, and many of its weird ideas, creatures and treasures could serve as excellent inspiration for D&D/OSR games of a science-fantasy or gonzo style. Here are some examples...
1. Vibro weaponry, similar to magical weapons but the +X to hit is instead added to the critical hit range, e.g. a +1 vibro sword would get +1 damage and crit on a 19-20.
2. When a character is brought back from the dead their visions of the horrific underworld will take a toll on their fragile mind, forcing them to endure possible insanity as per the system of your choice .
3. Yak Men pit fighters and witch doctors, owned as prized possessions by a mad, ageless tyrant.
4. A cat man assassin, deadly but extremely vain, pedantically counts the number of people killed and will boast of the exact number.
5. An Etherscope: a strange device that allows one to see into the void realm to search for and call spirits. Can be helpful for summoning a spirit from the realm of the dead for a ritual but you can also be unlucky enough to stare into the "face" of a formless horror, risking both sanity and soul. Here's one way of handling it mechanically:
Roll 1d20 (add INT and half your wizard/necromancer level): Natural 1: a Being of Law! They see you back and will judge you severely. If you are incredibly sinful/Chaotic, they may send a vision to a paladin to hunt you down. 2-10: Nothing besides strange cosmic phenomena (swirling colours, strange beings with trumpets, etc.). 11-19: A spirit! You may call it to you for questioning, rituals, or whatever reason you may have. 20: An unfathomable horror!
Yes, this does mean that wizards/necromancers technically have a higher chance of seeing a horror. Being a powerful wizard draws the attention of those sort of things so I think its appropriate.
6. A very valuable and highly realistic picture of the most divinely beautiful king or queen who ever lived, unclothed. If looked at, save vs a heart attack. A failed save means being reduced to 1HP (or 1/4th if you want the effect to be less harsh), otherwise you may just need a cold shower. Could be employed as a weapon in a manner similar to the Monty Python funniest joke in the world sketch or possibly sold to someone or something that has a way to resist its effect.
7. A Mutation Tomb: Possible stat increases, possible stat decreases but most important of all: possible mutations or becoming a mutant class . Here is a quick example table:
1-2: Decrease a random stat by 1.
3-4: Increase a random stat by 1.
5: Gain a random mutation.
6: Become a mutant class.
8. All of the deities of the campaign setting are actually extremely powerful, multi-animal hybrid  bio-weapons with incredible psionic power. All cultists receive psionic emanations from their deity, which can then be manifested by the cultist as specific psychic powers or "miracles". These "gods" also have differing opinions on how the cycle of life and death should be ordained, with each deity ultimately deciding on whether their followers should have the power to control the hellish, unnatural and undead or the power to destroy ("turn") them.
 Call of Cthulhu obviously has great insanity rules but there are other games and house rules that do it brilliantly, such as Warhammer Fantasy Roleplay or the rules found here: http://killitwithfirerpg.blogspot.ie/2014/03/insanitys-holding-your-pc-back.html.
 Mutant Future, The Metamorphica and Warhammer: Realms of Chaos: Slaves to Darkness are just some examples of the many great resources for mutants and mutations in RPGs.
 For the classic Egyptian mythology feel, different animals should be combined to make a humanoid deity. However, there is also the option to go nuts and combine monsters you choose from whatever monster books you have. Limit yourself to say 1D3+1 parts of the hybrid, get the page count of a monster book, grab an online dice roller and then roll a Dx (x being the total page count) for each part of the hybrid.