That right there? That's Sir Buttersworth. His hobbies include savoring life's most delicate fineries and single-handedly justifying the existence of Serious Sam 3's Steam Workshop support. Oh, and loping ever onward - to almost completely certain death - in dim hope of truly understanding that most top-hat-less of Others, Serious Sam. Can't forget that. But he is not alone, neither in that indirectly suicidal pursuit nor his presence on Steam Workshop. Sam's only just arrived on Valve's mod-friendly service, but his page is already impressively populated.
Despite the fact that the current top mod (as of writing) is, um, an axe imbued with no special properties or abilities whatsoever, there's some highly enticing additions on offer. Among others, you can queue up a megapack of survival maps, a smattering of classic weapons, a cardboard box to cover up the Harpy's horrifying multi-mouth, and a tiny weaponized version of the Scrapjack baddie who'll fire rockets from the palm of your hand. Also, there are anime characters with neon-hued hair colors because The Internet.
If you're interested in tossing up something of your own, Croteam's put together a handy step-by-step wiki to help get you started. And if not, well, someone has to destroy all these wonderful creations. I don't want to get your hopes up, but it could be you. I mean, do you have what it takes to not spend any money and click a couple buttons? Be honest with yourself, now.