These are what I consider “forgotten gems”. Most of them are pretty old, some decades old, but all of them have small passionate playerbases that have stuck with them because they are good games.

Brigador - isometric blow shit up in a cyberpunk dystopia with a huge array of tanks, mechs and hovercraft. Nearly a perfect experience especially in conjunction with its banger soundtrack by Makeup And Vanity Set.

Eador Genesis (with New Horizons mod optionally) -. Like Heroes Of Might And Magic 3 with tactical turn based combat like Kings Bounty. The game is TIGHT though and very hard and a campaign consists of many shorter games instead of one long slog which is way more fun in my opinion. Hard to learn because manuals and info is sometimes sparse but well worth it. There are newer Eador games but honestly I LOVE the retro graphics of Genesis, it makes the game simple and clear to read at a glance.

Cataclysm Dark Days Ahead - Simply put the best realistic apocalyptic zombie game in existence. So much mechanical depth and breadth it honestly makes it hard to return to a game like Project Zomboid because Cataclysm allows you to be so creative in your approach to situations and the enemy variety is super high. In continuous development in so many simultaneous directions it will make your head spin. Try the Sky Islands mod/mode if you want a more focused survival experience instead of a sandbox.

Winspww2 or Winspmbt - A decades long continuation of Steel Panthers 2, a tactical turn based war game. The once and future king of turn based tactics games of any genre. It is difficult to google stuff about these games because not a lot of people play them anymore and they are ancient software, but they are just such damn good turn based games with so many deep mechanics (especially scouting, artillery, speed based vulnerability and morale) that they are really in a league of their own compared to other turn based tactics games in general, not just realistic military simulators. I recommend Winspww2 because I think ww2 is more fun and suited to turn based combat but either is good.

Xonotic - another oldie, renamed from Nexuiz a couple of years ago, Xonotic runs on a heavily modded Darkplaces engine which is the original Quake engine at its heart. Xonotic is FOSS and plays like Quake but with Unreal Tournament style guns all with fun alt fires. Xonotic is a superb game, is super easy and fast to install and is an absolute blast. Try watching some high level duel videos in Xonotic, the speed and flow are incredible. Also Xonotic has hands down the best rocket launcher in multiplayer video games, no contest.

Beyond All Reason - BAR itself isn’t that old but it the latest in a long line of mods inspired by the rts Total Annihilation (which itself could arguably be on this list) and running on the open source Spring Engine (released in 2007) that have all cross pollinated ideas and balance tweaks over the years. There have been TA like games on the Spring engine for years and years but BAR is really a step up in polish both gameplay and UI wise. The AI is pretty damn smart too. One really fun addition to the TA formula is totally destructible terrain, it doesn’t wildly change the gameplay but heavily fought battlefields become more and more difficult to pass through at bottlenecks and it just adds to the atmosphere.

Supreme Commander Forged Alliance Forever - Another rts inspired by TA, though this game has battles on a way bigger scale. Aircraft fly like planes, they don’t just act like a hovering land units, serious artillery can send shells halfway across the map and battles are HUGE. Forged Alliance Forever is a community project to maintain Supreme Commander. Supreme Commander 2 might as well be in a different genre, it shouldn’t have the same name.

Remnants Of The Precursor - a fanmade remake of the original Masters Of Orion, the original space 4x game. This remake has a much better UI than the classic and has many subtle tweaks that have come out of the wisdom of fans playing MOO over and over again and knowing what should be changed and shouldn’t.

Panzer Marshal - a fanmade remake of Panzer General II, this is a turn based ww2 tactical game. It is MUCH simpler and more chill than Steel Panthers/Winspww2. This game is a blast and actually can run in a web browser (https://panzermarshal.com/). Also it has a touch interface, runs on Android and iOS and I think would be a blast on a tablet.

Forgotten Hope 2 - An old Battlefield 2 mod with fairly realistic ww2 combat that has very detailed and historically researched scenarios. Somehow, this mod is still in active development after all these years and at this point it is a damn good multiplayer shooter with vehicles.

Transcendence - An open world 2d top down space exploration game with a fleshed out world with factions, quests and a main story to pursue. I think it was released in 1996 so this game is pretty old but it is STILL in active development. Not very well known, but very well loved by people that know it.

Rain World - An utterly unique sidescrolling survival game where the enemies are driven by sophisticated AI protocols. Enemies just don’t sit there, doing nothing but patrolling a set path and waiting to fight you, they migrate across the map searching for food and fighting rivals. This means that sometimes you get VERY unlucky and open a door into a room with a bunch of tough monsters right in front of you and die, but the game doesn’t punish dying much really and the overall atmosphere of the game is incredible. This game is starting to receive more critical attention but it is criminally under appreciated for being so arrestingly unique.

Vintage Story - Not that old, but worth a mention for the fact that Minecraft is a gargantuan phenomena without really any other games trying to genuinely walk down the same path… except Vintage Story. Vintage Story started out as a survival focused modpack, focused on working through the stone and iron age, but eventually jumped ship from Minecraft and became its own game. One of my favorite parts of Vintage Story is the chiseling mechanic. Cosmetic blocks (about the same size as minecraft blocks) can be cosmetically chipped away so that they still are just a normal block to the game engine, but visually can become virtually any shape/pattern players want. It makes building so much more fun. I am very thankful Vintage Story exists as a Minecraft-like that isn’t controlled by a huge company like Microsoft.

The Original Peggle and Peggle Nights - Popcap ceased to exist the moment EA bought them, fuck EA, but all of Popcaps original games before they had their spinal cord harvested and extracted by EA execs are amazing, Peggle perhaps being the best. I feel like they should have this game running in hospital waiting rooms because it is such a calming experience to play Peggle. It is like a slot machine except if the slot machine loved you and didn’t want to hurt you or take your money.

Farm Together - Not old, but demands a spot on this list for being so underrated. Farm Together is a perfect co-op splitscreen arcadey faming game. Everyone always recommends Stardew Valley or Animal Crossing but Farm Together is a much more focused game on farming. There isn’t a story, tutorial, energy levels or anything else to get between the player and farming. You just pick the game up, start planting stuff and go which makes it VERY successful at roping reluctant co-op gamers in to play. What makes the game such a gem is that at no point is the game ever interested in stressing you out or punishing you and yet there is still a very real challenge to building out your farm in the most profitable way possible. Crops take real time to grow, so it plays a little bit like Farmville… except Farm Together wasn’t designed like a toxic addictive drug. If your crops finish, they just wait until you harvest them, they don’t go bad. Very underrated and easy to pass over because the graphics make the game look far more generic and half-assed than it is.