Here’s my full list:

Each subsection has my favourites near the top, then aren’t really in order.

Complete LitRPGs:

Threadbare series (including Small Medium and Dragon Hack) by Seiple (suggested order: trilogies TB1, SM, DH, TB2)
Limitless Lands by Henegar
Master Hunter K by From Hell
World Tree Online by Hooper
New Game Minus by Lin (and Street Cultivation, but it’s not a LitRPG)
Light Online by Larcombe
Eternal Online by Reynolds
Retired S-Rank Adventurer by Wolfe & Falcon
Life Reset by Kuznits
Blessed Time and Viceroy’s Pride by Plamann
Towers of Heaven by Milan
CivCEO by Karevik
Forever Fantasy Online by Aaron and Bach (great series, but very limited progression; max level from the beginning)
This Trilogy is Broken (a.k.a. This Quest is Bullshit! from Royal Road) by Valentine (a.k.a. Nixia)
War Aeternus by Dean
PrimeVerse by Billiau
Everybody Loves Large Chests by Iliev (NSFW gore, nudity, demons raping each other but asexual protagonist doesn’t understand sexuality and is mostly uninvolved)
Somnia Online by Hanna
The Dungeon Alaria by Kern
Rise to Omniscience by Oster
The Idle System by Pegaz
Last Born of Ki’darth by McGowen
Accidental Traveler (two complete trilogies) by Davis
Savage Dominion by Chmilenko & Penman
The Last Warrior of Unigaea and The Feedback Loop by Cooper
Factory of the Gods (a.k.a. Keldora) by Raizman (complete arc; once Dinosaur Dungeon concludes, this series will continue.)
Nova Online by Knight
Axe Druid by Johns
Tower Climber and Arcane Kingdom Online by Tanner
Emerilia by Chatfield
Euphoria Online by Tucker
Aether Gate Online by Hultberg
Chronicles of Ethan (and standalone sequel Overpowered Howard) by Monk
System Apocalypse™, Adventures on Brad, and Hidden Wishes by Wong
Combat Codes by Darwin is great, but it’s /r/ProgressionFantasy
Below here I haven’t read yet:
Death’s Mantle by Cooper
Space Seasons by Chapman
Heroic Villain, and Bathrobe Knight by Dean
Metagamer Chronicles by Hunter
Fall of the Black Seraph by O’Kelley (a.k.a. The Genesis Game by Locke)
Afterlife Online by Finn
The Iron Teeth by Straughan
Dungeons of Perdition by Basu
Pangea Online by Rowland
The Weaponized by Deckard
Never Die Twice and Kairos by Durand (a.k.a. Void Herald on RR)
Headshot Online by Siege
Trinity of the Kairos by Sinclair
Chronicles of Wycon by Moore
Abduction Cycles by Cressman
They Called Me MAD and The Houndsman by Pal
The Bright Lord by Knowles
Nora Hazard by Corvin
Beast Realms by Jones
Arena Manager by Opo
Frostworld by Peel
Magnus by Prime
Metamorphosis Online by Grey
Alterlife by Moss
Underverse by Cajiao
The Orzare Chronicles by O Toole
Alpha Physics by Kozlowski
Legends of Ascension by Hultberg
Badges of Dorkdom by Hodges
Star Divers by Landry
Legendary Farmer by Elizabeth Oswald
Class Shift by Sean Oswald
Ten Realms by Chatfield
The Weight of it All by Thorn
Phase Shift by Johnson
Voidbringer Campaign by Hall
Sky Realms by Osgood
Cultivator vs. System by Valerios
Uniworld Online and Glendara Awakens by Brooks
Freedom Online by Lingard
Enora Online by Adams
Harbinger by Keene
Bad Luck Charlie (a.k.a. Dragon Mage) by Baron
Apocosmos by Gkirgkiris
Real-Time Starcommander by Gregory
Dungeon Realms by Yang
Death’s Favorite Warlock by Dean
The Game of Gods by Kern
Tower Apocalypse by Cassius & Tang
Real-Time Starcommander by Gregory
Hack, Slash & Burn by Herzman
Cowboy Necromancer (some novellas to follow) & Tokens & Towers by Cooper
Apocalypse Gates (and I think other series) by Schinhofen (I’ve heard there are lots of sex scenes and he’s known for “secret harems”)

Standalone LitRPGs:

How to Defeat a Demon King in Ten Easy Steps by Rowe
Tales from the Upgrade by Henegar
The Card Job by Falbo (I used to also include The Crafting of Chess, but it now has a sequel. Regardless, it’s already a complete story in 1 volume.)
Leveled Up Love by Wong and Marshall
Battle Spire by Miller
Kaiju: Battlefield Surgeon by Dinniman (trigger warning: gore, abuse of various types)
Below here I haven’t read yet:
Zombie Slayer by Milan
Axilon99 by Cox
The Ridden by Kern
Aether Frontier by McCoskey
Royal Bodyguard and Just A Bronze by Richter
Hazelhearth Hires Heroes by Willison
Nigmus Online by Barnett
An Old Man’s Journey by Allanther
Toothless by Thomas

Sci-Fi LitRPGs:

(this is my attempt to include science fiction stories with LitRPG elements, but that focus on the science-fiction implications of VR/AI/games, not on progression)

Continue Online by Morse
Virtual Realities by Schott
Puatera Online by Chapman (the first three books have very little /r/ProgressionFantasy elements; later books are a bit more typical of the genre)

Series that can be read as complete with a midway stopping point, but have been continued:

The Gam3 by Yap (a sequel series started in August on RR, but book 3 ends a complete story)
Nova Terra by Ring (to be continued in Forgemaster )

Series that are on permanent (?) hiatus but at a stopping point that could be an ending:

Desire by Milan (not harem… Really poorly-named series! Milan calls it complete, but it’s an open ending.)
Monster Hunter NYC by Cooper (harem)
Below here I haven’t read yet:
Greystone Chronicles, Shadow Sun, The Darkelf Chronicles and Mars System Reboot by Willmarth

Dungeon core series:

Elemental Dungeon (a.k.a. Bone Dungeon) by Smidt
Dungeon Crafting, Dungeon Fairy, Dungeon World, Station Core, Dungeon of Chance and Holiday Dungeon Core by Brooks
Derelict by Henegar (complete trilogy; more books to come)
Divine Seed (a.k.a. Tree Dungeon) by Karevik
Bio Dungeon by Logue and Brooks
Divine Dungeon by Krout (imho stronger as a complete trilogy, but it’s also a complete series at five books.)
Guild Core by Reynolds
Futuristic Dungeon Core by Grant
Below here I haven’t read yet:
A Lonely Dungeon (RR) by cathfach
Cat Core and War Core by Henegar
Blue Core by InadvisablyCompelled (adult content chapters marked; I assume so they can be skipped)

Complete web serials:

Worth the Candle by Wales
The Infinite Labyrinth by Vincent Archer
The Humble Life of a Skill Trainer by altonsleet
Mother of Learning by nobody103 is amazing, but it’s /r/progressionfantasy not LitRPG.
Below here I haven’t read yet:
Vainquer the Dragon by Void Herald
Azarinth Healer by Rhaegar (book 1 on KU, epilogue to follow still)
Everybody Loves Large Chests by Exterminatus (trigger warning: rapey demon sex, gratuitous gorey violence) (also Small Chests Are Fine Too) more NSFW than KU version?
Epilogue by Etzoli
Damage=MA: A Rolling Stone LitRPG by zechamp
Death Singer by geminirand Or maybe just peruse COMPLETE-tagged stories on Royal Road.

Russian-translated complete LitRPG series:

Level Up by Sugralinov
Dark Herbalist by Atamanov
The Way of the Shaman by Mahanenko (ending on book 6)
AlterWorld by Rus
Below here I haven’t read yet:
Galactogon by Mahanenko
Animus and Chronicles of KieraFreya by Anderle
Mirror World by Osadchuk
Realm of Arkon by Akella
An NPC’s Path by Kornev
The Neuro by Livadny
Clan Dominance by Mikhailov
The Final Countdown by Ulengov

Asian translated LitRPGs:

Master Hunter K (on KU) by From Hell
Solo Leveling/I Alone Level Up by Sung-Lak
Infinite Competitive Dungeon Society and Everyone Else is a Returnee by Toika
The Legendary Mechanic by Peija
Seoul Station Necromancer by Jin
Rebirth of the Thief Who Roamed the World by Mad Snail
Reincarnation of the Strongest Sword God by Lucky Old Cat
Emperor of Solo Play by D-Dart
borderline LitRPG: Throne of Magical Arcana by Cuttlefish That Loves Diving
A Returner’s Magic Should be Special by So-Nan
Below here I haven’t read yet:
Demon King by Toika
Advent of the Archmage by Mo Xiang
Night Ranger by Dark Blue Coconut Milk
Warlock of the Magus World by The Plagiarist
Desolate Era by I Eat Tomatoes
The Second Coming of Gluttony by Ro Yu-jin
And there are a lot of complete translated cultivation web serials; search over at /r/ProgressionFantasy or /r/NovelTranslations for recs.
I also expect this list is missing many complete series. Please recommend any you think are worth reading!

#Harem series

World Seed by Miller
Reborn by Jackson
Reborn as a Baron Lord by Yang
Wolf King’s Lair by Drake

I’m likely going to GDPR-Nuke my Reddit account, depending on how things shake out by July 1, so not sure how to share this back with /r/LitRPGs. Is it easy to link to here from Reddit? idk