http://www.ragingmole.com/RTC/A one man project by George Gilbert, Return to Chaos is, as the topic title suggests, a remake of the very old "Dungeon Master" game, which is a first-person, real-time RPG. I understand it's similar to "Ultima Underworld" in a few aspects, though I haven't played that yet myself. RTC isn't open-source, but it is freeware and allows a person to easily create their own adventures with a *very* powerful yet rather easy to use editor.
As for the primary adventure, identical more or less to the one in "Dungeon Master", you play as the apprentice of The Grey Lord. You can read the full background on the RTC site, but the gist of it is: your master attempts to reunite the power gem with the Firestaff and restore the artifact to its former glory, but something goes wrong. The power unleashed rips his master into two distinct beings, essentially Lord Order and Lord Chaos. The former of these two asks you to retrieve the Firestaff from the dungeon and banish Chaos, and the game features at least two possible endings depending on your exact actions.
Except there's one problem. Theron isn't exactly material anymore, after that accident, and can only lead a party. You explore the Hall of Champions, filled with Heroes forever trapped in mirrors, and release up to four of them.
Some notable features:
* Four classes, Fighter / Ninja / Wizard / Priest, if I recall the names exactly. Wizards and priests cast spells by entering a series of runes. The priest's main draw is his or her ability to make potions of various types, as spells, provided they have an empty bottle. Warriors kill things, as you may have guessed, and ninjas have a knack for throwing things.
* Non-linear development. Characters can level up in
any class by trying to use that classes specialty. Have your warrior attempt to cast mage spells for a while (if he has enough mana for even the cheapest one) and watch as he slowly becomes an apprentice. Throw items with your mage and notice his growing skill as a ninja.
* Hunger / Thirst. The dungeon denizens are bad enough, but you'll also have to practice basic survival. Food can become hard to come by.
* Really, really cool items. If you throw something, it'll sail in the direction, covering a distance I believe determined by the item's weight, your strength and possibly a third aerodynamic trait.
* That really handy editor would allow you to make adventures even outside of dungeons, with enough power behind it to make some really wicked things. I've made a store, a bank and a cutscene with relative ease. It can be a bit tricky to get the hang of if you've never used anything of the sort before, however.
* Besides the "Dungeon Master" story, the game also includes a remake of "Chaos Strikes Back" (the expansion of sorts, expecting you to import characters but not requiring) and "Dungeon Master 2", a very detailed romp both indoors and outdoors, with weather effects, stores, more spells and so on.
* The remakes of the classic games are open-source, so you can open them in the editor and make any adjustments that amuse you. Make a spell that summons apples so you can avoid starvation, or place a custom-made sword on a special level. Or, make your own characters to add to your party.
There's more to it then this, but you can read more accurate and detailed information on its site. It's great fun, and if you dig around the forums I bet you can scare up some user-made adventures. If the retro-ish graphics aren't to your liking, you could try the Dungeon Master 2 game first- but I would recommend playing the original before that one.
Edit: Oh yeah, I didn't even mention the puzzles, traps and so on. There's more here then just mindless monster bashing. Running in fists-flying will get you killed later, as one of my (least) favorite monsters can launch lightning bolts straight down hallways before you even SEE them. It gets very tense later on!