DISCLAIMER: This is not an official list. This is based mostly on my own findings and memory. This writing likely has mistakes and missing information.
Ok, so here is a list of UD games that have existed in the past (or still exist), based on what I've found on the profiles of the devs and by digging through my old notes.
This list does NOT include upcoming games (Harriston, Fontana Dam, Johnsboro etc.)
I've divided the list into 'generations' to make it more readable. The division is NOT based on anything official, it's about when they were made, and how advanced their 'game systems' are.
Unfortunately, some games do not have links, usually because the dev's inventory isn't public and Roblox has a retarted search system, the game has been overwritten with something else, or other reasons.
This list was last edited December 2019.
As far as I know, these are the first UD games ever. At least I haven't found anything older anywhere. Their place slots have likely been overwritten multiple times by now, but Alex/TTP has released them as models.
This gen likely had more games, but these are the only ones I've found.
New Bloxia (unsure if this counted as an UD game)
Still, my info on these early days is very limited. I only found one game of this gen by digging through TTP's alts.
Ok, I think we're now in 2012-2013 or something. At least based on the fact gamepasses became a thing in late 2012 and this generation has/had the first gamepasses.
New Bloxia (again, unsure if this was an UD game, though it did use the UD systems)
Note that I'm not sure whether this and gen 6 should be separate, their game systems differ but there was overlapping in the supposed connections.
Another note, the game connections are based on some old notes I had taken years ago, I think they were originally written in the games' descriptions, though it isn't possible to verify that anymore.
Connections: UD IV in South, UD VI in West, Trenton in North, Sherbrooke in East.
(no link, was made on Marcus's old account, which has been terminated)
Connections: UD III in East, UD IV in North, Burlington in West
(I'm not sure why Burlington would be in the Southwest, perhaps there is a mistake in my old notes?)
(no link, likely overwritten by newer version(s) of Burlington)
Connections: Jackson in East (again, not sure about this one)
I joined Roblox during this gen. I first spawned in UD II, at Red Mill Crossroads. Even in today's Odessa I prefer to buy a house there, so I guess it's my UD hometown. This gen has a functional 'teleportation' system between UD II and UD III.
Connections: UD III in West, UD IV in North
Connections: UD II in East, UD IV in North, Jackson in West
NOTE: this game has since received the gen 7 update.
Connections: UD I in north, UD II, UD III and Jackson in South, Fairfax in East, Oakwood in West
(again, Fairfax seems a bit odd)
This game was never released, though its existence is seen in the connection notes.
Connections: UD VI in South
Again, unreleased. Might've been the predecessor of Delancy Gorge, based on the location.
Connections: UD I in east, UD V in North
Was going to be the first UD game by Matt/Zeffy.
Connections: UD I in South
This one was being made by Ren97.
Connections: UD I in West
Connections: UD IV in West (maybe possibly potentially)
Briefly named 'Vermillion' before the discontinuation of gen 6.
Connections: UD IV in East
Called 'The Universe Update', instead of separate games each developer had a 'universe', from which players could teleport to different games. I recall it was scrapped because Roblox's teleport system was somewhat unstable.
Unfortunately the side effect of using universes means many games of this era don't have links here.
Mid-Atlantic Driving Universe
no link, sorry
Originally called 'Ultimate Driving II'. The link goes to current Westover.
That link is for a 'rehost', with new game systems.
no link, sorry
That one's also a 'rehost'
That one was tested in UD IV's slot.
Classic UD II & UD III
Not a 'true' gen 7 game but used the same game system. It was basically gen 6's UD II and III joined together with a new Interstate in between.
Southern Driving Universe
The games were Stone Mountain, Forsyth and Atlanta, but the links are lost in time.
New England Driving Universe
Again, I don't have links. Only game I know of is Burlington, and that one has probably been replaced with the newer Burlington.
Arizona Driving Universe
Afterwards, Preston changed the name to Calizona, later to Calizonavada, and even later to Southwestern Driving Universe.
Only games I have notes of are Phoenix and a new version of Vermillion. Obviously there were more planned, hence the universe name(s).
Virginia Driving Universe
Fairfax is the only one I recall seeing during this gen. There might've been something else too.
Western New York, Ontario and New Jersey Driving Universe
Yes, this is the one that got nuked by Matt's PC and that's what the 'Impact Crater' on the UD website's map is about.
Was apparently going to be the biggest game of UD, but failed. Matt actually released this game somewhere on the forums, but I can't find the thread currently.
There were potentially other games here. My old notes mention Trenton but that's it.
Quebec Driving Universe
For some reason I have literally no info about this one. The only thing my notes have is 'sherbrooke?'.
This is the 'current' generation of UD, with stats shared across the games, mini maps and other fancy stuff.
Any discontinued games in this gen are
Based on the gen 7 Westover. Notable changes include rotating the map and route renumbering.
This is the original gen 8 Odessa, which was replaced by the current one.
Harriston Bay Bridge & Tunnel. Was merged with Westover.
Savannah (replaced with Watkinsville)
Old Town Beach (as of 2019 this slot contains Narragansett)
Hudson Landing & South Burlington (no link)
Falmouth Bay (no link)
Manchester (no link)
Middlebury (no link)
Portsmouth (no link)
Fort Trumbull (no link)
Rocket trucks, infinite speed, negative bounty (I still have it!), confederate limo and so on...
Sandy Beach (no link)
Edinburgh (no link)
Meade Hills (no link)
Elk Mills (no link)
Masonsville (no link)
Springfield (no link)
Ponderosa Valley (no link)
Council Bluffs (no link)
Pleasant Valley (no link)
Arlington (replaced with Port Darwin)
Des Plaines (replaced with Beach Park)
Peoria (replaced with Anderson)
NOTE: I'm not sure if this is actually the correct one.
French Broad(NOTE: I'm listing this because it appears to be cancelled)
Hilton Head Island(same as above)
Waxhaw(likely a leftover from when Waxhaw was planned to be removed from Monroe)
New Hartford (like New Bloxia, this has UD systems [as of July 2019] despite not being an UD game)
Total: 121 known or strongly suspected UD games. That's a lot!