| Underspace (2024) | 326,903 | 222 |
| Understanding, The Game (2020) | 2,563,849 | 162 |
| Undertale (2015) | 21,597,690,828 | 545,493 |
| Undertow (2007) | 4,854,887 | 492 |
| UNDERWARD (2025) | 889,400 | 253 |
| Underwater Diving (2024) | 101,393 | 24 |
| Underwater hunting (2018) | 6 | 3 |
| Underwater the Game (2009) | 347,900 | 46 |
| Underwater Wars (2021) | 6,783 | 16 |
| Underwater World (2021) | 22,390,789 | 317 |
| Underwater World - Idle Desktop Colony Building Simulator (2022) | 336 | 1 |
| Underway (2022) | 937,620 | 244 |
| Underworld Ascendant (2018) | 4,096,706 | 823 |
| Underworld Dungeon (2017) | 29,745 | 19 |
| Underworld Explorers (2024) | 0 | 0 |
| Underworld Idle (2021) | 2,716 | 20 |
| Underworld Island (2022) | 373,670 | 161 |
| Underworld Office (2020) | 2,369,038 | 384 |
| Underworld Overseer (2024) | 28,208 | 18 |
| Underworld Re: Card (2022) | 30 | 1 |
| Underworld: The Eternal War (2004) | 435,703 | 213 |
| Underwurlde (1984) | 68,038 | 70 |
| Underzone (2020) | 22,386 | 35 |
| Undesired Catch (2024) | 148,785 | 8 |
| Undesired Shift (2023) | 0 | 0 |
| UNDETECTED (2022) | 4,325,016 | 1,074 |
| The Undisputables: Online (2021) | 45,987 | 28 |
| Undivine (2025) | 7,431 | 42 |
| Undoing Evil (2022) | 0 | 0 |
| UnDungeon (2021) | 1,606,948 | 802 |
| Undusted: Letters from the Past (2025) | 166,450 | 113 |
| UnDuster (2024) | 59 | 3 |
| UNDYING (2021) | 37,973,247 | 7,382 |
| Undying Fortress (2025) | 174 | 1 |
| Undying Harvest (2024) | 0 | 0 |
| Unearned Bounty (2018) | 253,890 | 88 |
| Unearthed Inc: The Lost Temple (2016) | 15,149 | 17 |
| Unearthing Colossal (2016) | 6,505 | 9 |
| Unearthing Invasions (2024) | 0 | 0 |
| Unearthing Mars 2: The Ancient War (2018) | 61,987 | 121 |
| Unearthing Process (2019) | 0 | 0 |
| Uneasy Memories (2024) | 196 | 3 |
| Unending Dusk (2019) | 10,694 | 16 |
| Unepic (2011) | 7,382,202 | 7,764 |
| The Unexpected Quest (2020) | 368,700 | 406 |
| Unexplored (2017) | 4,307,195 | 1,095 |
| Unexplored 2: The Wayfarer's Legacy (2021) | 610,079 | 296 |
| Unfabulous (2006) | 227,751 | 55 |
| Unfair Jousting Fair (2015) | 488,784 | 18 |
| Unfair Rampage: Knightfall (2025) | 584 | 9 |
| The Unfallens: Awakening (2023) | 1,842 | 48 |
| Unfinished Dream of All Living Ghost (2023) | 8,597,333 | 2,095 |
| The Unfinished Swan (2012) | 3,516,449 | 2,486 |
| The Unfinished Swan (2020) | 7,323,388 | 969 |
| Unfinished Tales: Illicit Love (2012) | 35,942 | 43 |
| Unfolded : Camellia Tales (2021) | 2,905 | 21 |
| Unfolded Cube (2024) | 36 | 2 |
| UNFOLLOW (2023) | 3,711,366 | 665 |
| Unforeseen Incidents (2018) | 1,019,564 | 1,387 |
| Unforetold: Witchstone (2024) | 237,603 | 52 |
| Unforgettable Voyage (2023) | 1,086 | 10 |
| Unforgettable You (2021) | 246 | 8 |
| Unforgivable: Eliza (2018) | 13,164 | 7 |
| Unforgiving Trials: The Space Crusade (2016) | 65 | 2 |
| Unforgiving: A Northern Hymn (2017) | 24,072,463 | 2,510 |
| Unforgotten: Ordinance (2025) | 9,079 | 62 |
| Unfortunate Spacemen (2020) | 7,377,069 | 1,274 |
| UnFound (2021) | 3,635 | 9 |
| Unhack (2015) | 12,636 | 51 |
| Unhack 2 (2017) | 759 | 13 |
| Unhappy Ever After (2017) | 4,557 | 19 |
| Unheard (2019) | 3,674,556 | 1,180 |
| UNHEIM (2024) | 509,542 | 94 |
| Unhinged 2 (2025) | 5,356 | 15 |
| Unholy Alliance - Tower Defense (2021) | 859 | 16 |
