"In the grim dark future of the hobby there is only Grimdark Future" - onepageanon
Grimdark Future is a single-page ruleset made for 28mm miniatures, namely Warhammer 40,000. Legend says that a long time ago the people at One Page Rules used to make a game called 1p40k, but once they got scared of getting the C&D hammer they re-named everything and now we are here. They also launched a patreon page to make some money, so probably that's why they changed the names in the first place.
The fluff of Grimdark Future is pretty simple: humanity on earth split into two major factions, one faction believed in jesus and one believed in science. They had a great war and threatened to blow the whole place up, so colonization ships were shot far into space to escape this madness. The ships landed in a place called the sirius sector, where humanity met other alien species and realized they were fucked, so back to war it is.
The gameplay is basically 40k-lite, units have only two stats (quality and defense) and things are streamlined to the core. Even though things are kept pretty simple the battles feel like 40k and each army has its own distinct play style. The game is very portable as the rules fit on one sheet and the armies fit on another sheet, so no more carrying 9000 books around.