Each of my settings has its own themes which set it apart from the others. Some worlds which share similar themes are grouped together into triangles of three (or more) universes, which are detailed below:
1st Edition Settings (and to a lesser extent Thalasera)
Theme: Tropes
Settings: Yume-Honto (manga and anime), Hyakuopolis (science-fiction) and The Known Realm (high fantasy); plus Thalasera (seafaring adventure)
2nd Edition Settings (and to a lesser extent Dracromia-Metaligon)
Theme: Genres
Settings: Frontier (western), Feruyasei (monsters) and Tankensei (historical); plus Dracromia-Metaligon (pulp fantasy)
d20 Modern Settings (and to a lesser extent Junihoshi)
Theme: Eras
Settings: Terra Neos (contemporary), Tabitineris (far future) and Clefmath (classical); plus Junihoshi (medieval)
Rules Cyclopedia Settings (and to a lesser extent Incognes)
Theme: Fantasy races
Settings: Panarcha (halflings), Mekharatus (dwarves) and Nulmahou (elves); plus Incognes (gnomes)
D&D v.3.5 Settings (and to a lesser extent Panarcha)
Theme: Base classes
Settings: Thalasera (rogue, bard and ranger), Sunayuki (cleric, druid and barbarian) and Wyrmaria (wizard, sorcerer and paladin); plus Panarcha (fighter and monk)
4th Edition Settings (and to a lesser extent Terra Neos)
Theme: Worlds
Settings: Dracromia-Metaligon (alternate realities), Zokugemina (dual societies) and Pentorbix (planetary system); plus Terra Neos (other dimensions)
D&D Essentials Settings (and to a lesser extent Frontier)
Theme: Knowledge
Settings: Junihoshi (lore), Vitrumund (science) and Astrumium (technology); plus Frontier (discovery)
5th Edition Settings (and to a lesser extent Yume-Honto)
Theme: Popular themes
Settings: Incognes (magic), Periquos (time travel) and Kumorimbus (sky adventures); plus Yume-Honto (Asian fantasy)