If you ever thought that Saints Row IV just doesn't have enough ridiculously over the top weaponry, you'll be pleased to hear that Volition has just added Steam Workshop support! In other words, the ability to create, share, and download custom weapons, clothing, scripts and cheats, and a whole variety of other gameplay changes. The Saints Row IV Workshop only just launched so there isn't much available right now, but someone has already taken the time to make a flamethrower guitar... because why the hell not!
On the other hand, if you prefer to create rather than to simply use what others have built, you can find a basic guide and all of the necessary tools by heading over here. Do bear in mind that learning all of this is going to take you a little while, but should you manage to do it, the sky itself will be the limit!
And as an added little bonus, Saints Row IV and Saints Row IV: Game of the Century Edition are currently on a very steep discount on Steam. So if you don't own SR4 just yet, or if you want to get a couple of your friends hooked, now would be the best time to give it a go. Have fun!