Duke Nukem 3D is one of the best first person shooters created, and the Atomic Edition – the biggest version of the game – is currently free on GOG.
Grabbing it is simple, the page is here, and even if you’ve not created an account it doesn’t take more than a minute. When we tried it just then it also added a load of other freebies to the basket, so it’s well worth doing. Duke Nukem is only about 35MB too.
The game’s been available on countless formats, but the PC original is still the best (and this download installs along with DOSBox, so worked first time on Windows 7) and this version also supports mods and comes with an extra episode at the end – seriously, if you’ve not played it before just get it.