Max Heap
Call of Cthulhu.
But if you want D&D-like stuff try some of the OSR clones. They are usually cheap and easy to pick up and play. I recommend:
Swords and Wizardry - for a smooth like butter OD&D experience. It has race and class separated, and it has most of the classes that you might be familiar with from the IE games. The combat is phase based. It has rules for both ascending and descending armor class. Only one saving throw. Monsters are super easy to create. Nice and smooth like I said. The PDF is free. About 130 of rules. It has good support.
Basic Fantasy RPG - Another OD&D clone. Separate race and class, but the book only contains the four basic classes, but there are free supplements if you want more. 3 saving throws. It's pretty much like S&W at the end of the day. All the PDF's for it are free, but if you want to own a physical copy it will only cost you $5 !!!!! and the rest of its supplements are even cheaper. Instead of wasting $90 or what the fuck all 3 5e books cost, spend ~$20-30 on BFRPG books and you are set for life. About 150 pages of rules. Lots of support for it.
Lamentations of the Flame Princess - Yep, another OD&D clone, but slightly more thematic. Actually the rules are setting-neutral but the writing style and the artwork reminds one of weird fantasy, something like Lovecraft meets D&D. It has race as class, so elf, dwarf and halfling are classes onto themselves. Ascending armor class. It also comes with an interesting slot based encumbrance system that should be considered being added to any D&D type game IMO. The support is great, with some really, really interesting supplements. For example there's a supplement called Veins of the Earth which deals with underdark-type environments, its denizens, layout and stuff like that. Anyone running underground adventures should look into it and steal from it as much as possible. The PDF is free (without artwork). Again a short book at just about 150 pages. There's also a spoof spin-off title named Machinations of the Space Princess for your Buck Rogers/Roger Wilco campaigns. I have that downloaded but I haven't read it yet, just the first few pages. From what I've read it seems wacky as hell.
And last but not least Dungeon Crawl Classics - Technically this is not a retro clone. Mechanically speaking it is a very modified d20 game, but it has some of the trappings of older editions, for example it has race as class. The armor class is ascending, it has 3 saving throws, bla bla bla. The game emphasizes gonzo and wackiness. For example when you generate you character you start out as a level 0 schmuck with 1d4 hp which can be anything from a radish farmer, beggar, money lender or scrub. Each player generates multiple characters and then the whole party goes through what is called a funnel, a level 0 adventure from which only the strongest will survive. Those that do graduate to level 1. Congratulations. Magic is vancian but with a unique twist: you always roll to cast a spell. The better you roll the stronger the effect of the spell and you don't lose it. If you roll poorly you lose it for the day and if you roll a 1 bad things happen. Your fireball can explode into your face, the strength spell weakens instead and so on. It can also corrupt you, draining your attributes, giving you disabilities, cursing you etc. Cleric spells work similarly. If you roll a 1 your god is pissed with you and asks for atonement. The game is a bit more complex than the other systems that I've mentioned , but this is mostly due to its heavy reliance on charts (for spells, for critical hits and failure, etc.). It's NOT a number crunching game however. Just as with all the system that I've mentioned you really can't powergame since everything is rolled randomly at character creation. The tome is massive at 450 pages but most of it is tables for spells and other stuff. There's a post apocalyptic knock off called Mutant Crawl Classics that I am dying to try out. The rest of the support for it is also awesome. There are some really good modules such as Purple Planet which evokes a Might and Magic feel with it's mix of fantasy and sci-fi. Oh, it also uses some "funky" dice like the d7, d24 or d30 but they are easily simulated with "regular" dice.
What I like about these is that they are easy to read (being short, except for DCC), contain PHB, DMG and MM all in one neat little package, are easy to learn and to teach to others, and quick to run and play. If you want complexity then these are probably not for you but if you like old school then give OSR a try. There's tons and tons of OD&D and AD&D clones out there, so there's something for everyone.
Here's a cool vid on the subject:
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