Trenchhammer is a free fan rules hack for Trench Crusade, adding rules to build warbands from 25 different Warhammer 40k armies to the fast-playing and gritty core system. It's the work of Chris "Goober" Ramsley, a professional game developer who works for Evil Genius Games designing the Everyday Heroes tabletop roleplaying game line.
Ramsley states in the introduction to Trenchhammer that they made the rules hack because "I had the idea and it would not leave my brain until I wrote it down". Presumably they write really fast, because despite this being "Purely a passion project", on top of the 25 core Warhammer 40k factions with rules there are a total of 100 sub-factions and dozens of mercenaries. Even the wildest digital tiles in our list of the best Warhammer 40k games can't boast that level of modded diversity.
You can get the rules for Trenchhammer for free online. There's also a dedicated Discord server for the rules hack, which is a good place to look for other players or to get advice on the rules.
The game expands a little bit on the core rules of Trench Crusade, but everything new is an addition rather than a rewrite. There's a new system for Psychic powers (which work a little differently from Goetic magic), rules for burrowing movement, and a few new keyword abilities, most of which just add a granularity to weapons. It's all fully interoperable with basic Trench Crusade, so if you want your Trench Pilgrims to face off against the Death Korps of Krieg, or to have Chaos Space Marines duke it out with Heretic Legions, you can totally do that.
There's a full set of campaign content, including skill tables and campaign locations that tie in with the unique warbands. If you're playing as World Eaters and happen across a Blood Pit, one of your Elites can bathe in it, gaining a massive boon of skulls; or while most factions encountering a Black Market can strike a trade deal with it, the T'au and Genestealer Cults can subvert it to expand their diplomatic or genetic infiltration.
It wouldn't be a fan mod if there weren't rules for factions that either haven't had models since 1987, or have only ever existed in fan canon. If you want to play with a warband of Warhammer 40k Skaven, or even some surviving Slanni frogmen, Trenchhammer has rules for them too.
If you've got a Warhammer 40k warband and feel like giving this a go, we'd love to see pictures and hear tales of your games in the Wargamer Discord community. For a roundup of the best stories on our site each week, make sure you're subscribed to our regular newsletter.