Duke Nukem 3D: Megaton Edition
By 3D Realms - buy on PC, Mac, and Linux (£6.99)
Duke Nukem won fame for its humorous script and level of gore. But it managed to keep with with a diverse selection of interesting and amusing weaponry that encouraged tactical play.
You can drop pipe bombs on enemies from above, freeze them, even shrink them and stamp them underfoot.
By Number None - buy on PC, Mac, and Linux (£6.99)
Another recent game that won't demand much from your hardware, Braid was rightly celebrated for its narrative curveballs and rock-hard puzzle platforming.
You won't find many other games that manage to so demanding on your brain, your emotions and your twitch fingers all at the same time. It's frustrating but, as the designer said, if you manage to beat its challenges, you will feel very good about yourself.
By Re-Logic - buy on PC (£6.99)
A bizarre blend of exploration, action and Minecraft, Terreria offers incredible depth and variety for a game that runs on modest hardware.
If it's not enough to explore a procedurally generated world, fight boss monsters and attracting followers, you can even use your imagination to build elaborate machines.
Rome: Total War - Alexander
By The Creative Assembly - buy on PC (£2.99)
Total War hasn't managed to be a fixture on the gaming calendar since 2000 for no reason. Happily for the owners of older systems this entry from 2004 remains one of the very best.
It's a proper real-time strategy game with actual strategy in place of base-building races. Plus some good history too. So a winner all round.
Broken Sword - Director's Cut
By Revolution Software Ltd - buy on PC, Mac, and Linux (£4.99)
No retro-focused list would be complete without a classic point and click adventure. But on Steam, many of these have been enhanced or revamped to a level where they won't run on modest hardware.
Luckily, one of the best of the lot will. With a compelling plot and a diverse selection of logic and hidden item puzzles, it should keep you occupied for hours.
Unreal Tournament: Game of the Year Edition
By Epic Games, Inc. - buy on PC (£5.99)
This may be the purest distillation of frenzied shooting action ever made. It eschews niceties like narrative in favour of a vast range of maps and game types to play against real people online or skilled AI bots off it.
Plus, it's graced with a wonderful selection of enormous guns and ludicrous power ups.
System Shock 2
By Irrational Games - buy on PC, Mac, and Linux (£6.99)
A game this old shouldn't be this scary. You might want to give up during the opening sequence with its ponderous tutorial and dated graphics. But keep at it and you'll be rewarded with one of the most horrifying action games ever made.
It's another older game that regularly shows up in high positions on best of all time lists. And it's not hard to see why. All the limitations of the ancient video engine won't matter a jot when you're lifted out of your seat by a jump scare.
Deus Ex: Game of the Year Edition
By Ion Storm - buy on PC (£4.99)
When people compile lists of the best PC games of all time, this regularly comes near the top in spite of having been released in 2000.
It's the combination of the free-form way in which you can complete objectives and the knock-on effects of your choices that make it such a winner. The mix is almost as intoxicating now as it was back then.
FTL: Faster Than Light
By Subset Games - buy on PC, Mac, and Linux (£6.99)
Most of our picks on this list are older classics. But here's a modern game that's undemanding on hardware, but very demanding on the player.
It's got an addictive and unusual blend of rogue-like, strategy and choose your own adventure. The story is different every time you play, although it commonly ends with the horrible death of your entire crew.
By Valve - buy on PC, Mac, and Linux (£6.99)
If you're going to try and run a first-person shooter on a limited machine, you might as well start with the best.
Half-Life remains a pivotal moment in the history of video gaming. And it's old enough now both to run on weak hardware and to be unfamiliar to younger gamers. So there's no excuse not to have experienced this genre-changer for yourself.
Sid Meier's Civilization® III Complete
By Firaxis Games - buy on PC (£2.99)
Civilization fans will tell you to play IV or V in the series for challenge and accessibility respectively. However, if you can't run either of those, Civilization 3 still lets you easily connect to network games.
That means you can enjoy playing this incredible strategy franchise against your friends, however aged your device is compared to theirs.
Fallout 2: A Post Nuclear Role Playing Game
By Black Isle Studios - buy on PC (£7.99)
Everyone's talking about Fallout 4 at the moment. While you wait, why not remind yourself that the popularity of this series started long before Fallout 3 by playing this classic iosmetric RPG.
The interface might feel dated, but the post-apocalyptic setting is just as vivid, exciting and unusual.
X-COM: UFO Defense
By MicroProse Software - buy on PC (£2.99)
A contender for possibly the most-played older game on Steam. This was the inspiration behind the much more recent XCOM: Enemy Unknown and will be instantly familiar to fans.
It's nowhere near as accessible or pretty as its successor game. But it is much more challenging, offering enormous amounts of play hours for a tiny investment.
By Runic Games - buy on PC and Mac (£10.99)
Torchlight isn't all that old, but the devloper made a special effort to make it as portable as possible. It's got a special netbook mode which helps it run like a dream on older machines.
And while it might be tempting to go for the more recent sequel, this original has all the fun and charm which underpins the success of the series.