[my D&D sandbox]

My claims to fame:
I invented the word Psion.  (as far as I know)
I offered the name for the Official Mystara Fan Site (Vaults of Pandius), which was chosen by the administrator.
I did some mini-interviews with D&D designers in relation to Mystara. (The interviews are hosted at the Pandius site.)

My manifesto (what I strive to see manifested): From Open Gaming to Free Culture: For a Third Golden Age of roleplay.
D&D research and aspirations:
D&D Realities (the in-game effects of rules iterations)
D&D Worlds and their Timelines [unfinished]. For maps of all the D&D worlds see: Atlas of the D&D Worlds (P.S. here's a teeny map of the planet Nerath: http://forgottenrealms.wikia.com/wiki/World_Axis_cosmology) And this shows a theory for lining up the Nerath and world map: http://www.thepiazza.org.uk/bb/viewtopic.php?f=72&t=15210
Timeline correlations (Grand History of the Multiverse):

Mystara was, for most of its existence, not part of the Advanced Dungeons & Dragons multiverse as originally described in the Player’s Handbook and Dungeon Master’s Guide. It was the setting instead for the Dungeon & Dragons game, and grew from the module X1 Isle of Dread, which sketched out the world, and was included in all of the 1980 Dungeons & Dragons: Expert Sets. In 1994 TSR converted Mystara to the Advanced Dungeons & Dragons system and subsequently made some minor attempts to add it to the multiverse setting. 

In Domains of Dread the Dark Lord Meredoth is said to come from the Alphatian province of Norwold, arriving in 635 of the Barovian calander. (p79) But Norwold was not colonized by Alphatia until 919 AC according to Dawn of the Emperors (Bk III, p7). This would put Mystara wildly out of sync with the other campaign settings, and can be discounted as an example of Ravenloft’s famous mists transferring their victims through time as well as drawing them across planes. 

There are some Planescape/Mystaran cross-overs. The Planewalker's Handbook, set in 128 Ha (p53), describes the Alphatian Empire as “fallen” (p33). We know the Alphatian Empire disappeared from the surface of Mystara in 1009 AC as depicted in Wrath of the Immortals (p??). Additionally, Uncaged: Faces of Sigil, set in 128 Ha, describes a Shadow Elf, Farrow, as an inhabitant of Sigil (p32). Farrow is spying in the Great School of Glantri when a Glantrian mage forcibly sends him to Sigil through a gate. It is unclear how long Farrow has been in Sigil, but certainly a few years. This provides a broad link between current time in Planescape and Mystara.

There is an equally vague, yet direct, link between Mystara and Spelljammer. The introductory Advanced Dungeons & Dragons boxed set First Quest includes a Spelljammer adventure in which the antagonists are heading for the Rock of Bral (AdvBk, pp. 45-54). Karameikos: Kingdom of Adventure is contemporary with First Quest (p??) and is set in 1012 AC (this aligns with Poor Wizard’s Almanac III, also set in 1012 AC and published in 1994 like Karameikos: Kingdom of Adventure and First Quest. There is no indication that the Rock as mentioned is not contemporary with its description in SJR5 Rock of Bral, which is set in 5049 OC. This fits with the Planescape links above, as the fall of Alphatia in 1009 AC would coincide with 124 Ha. 

So we have 1012 AC linked to 5049 OC, which is 1367 DR. That would make 1361 DR equal to 1006 AC.

Also, "Blood War" mentioned in Dark Knight of Karameikos. And Harmonium paladin wears red steel.

Pluffet Smedger and the Fictive Frame [unfinished] (note that Smedger says Oerth is long gone.)
Culture Books: Oriental Adventures-style books for each real world culture.
Genre Books: covering D&D Modern, Past, and Future.
D&D Languages and Game Glossaries [unfinished]
The Nexus and the World Serpent Inn: including all homebrew settings and house rules in the meta-cosmology
The Un-Setting [unfinished]
Middle-earth and D&D:
  • Middenyard: a pluri-system open-source fictional world inspired by Middle-earth. With Open Game Rules based on the latest iteration of D&D as the first sample rules.
  • MERP Next: using MERP's conception of Middle-earth--and their official guidelines for converting to AD&D--as a straightforward high-magic gonzo dungeon-crawl D&D5e version of Middle-earth.
  • Middle-Oerth: The equivalent of Middle-earth as a fictional line of books within the Urban Arcana campaign setting.
OGNext: An Open Game for all Imaginative Worlds
CSG: Community Supported Gaming
D&D Ceremonial Communities. Basically, real world D&D religions, founded on the D&D pantheons as perceived in the light of humane wisdom (anthroposophy). Humane wisdom can discern the Truth, Beauty, and Goodness in even fictional legendariums and mythologies, and bring them to life as the imaginal wellsprings of real human community.
PnP RPG: A future social art
D&D Earth [unfinished]
D&D Animated Series game
Dragons in the Attic game (Lake Geneva in D&D Earth)
D&D coins
Frank Mentzer's World of Urt: An alternate Mystara using only the sparse setting information from the BECMI rules set, and the Masters World Map.
Old 5E playtest sandboxes
Domains as deities Update: thankfully, the hamhanded generic deities of the first playtest were dissolved. 5E domains are held by multiple deities, and Life domain is accessible to all non-evil clerics.
subclasses Update: My sandbox was compiling all the subclasses I heard of during the playtest. The final selection in the 5E PHB is pretty different.
Background in 5e (based on real world human cultures) Update: 5E does feature human ethnicities as a counterpart to the demi-human sub-races.