While I am far from an expert on medieval weaponry, and I appreciate artistic license, there are some weapons proposed for D&D 3.x that just seem mind-bogglingly impractical. Perhaps somebody can point out the utility of some of these beyond being "kewl."
1) Whip-daggers: Did anybody ever actually create such a weapon? Whips strike me as falling into the category of "agricultural tools used as improvised weapons." What would be the point of tying a dagger to the end of one, rather than just learning to throw knives?
2) Sugliin: Here you have a big wrack of sharpened antlers so unwieldy that you have to spend two feats just to use it as a normal weapon. The tactical problems for this are mind-boggling, especially given the fact that you'll probably draw the eye of every archer in sight.
3) Mercurial Swords: Explain the attraction of a using a deliberately unbalanced weapon that is likely to spew a highly toxic substance if sundered.
4) Orc Shotput: The perfect counterpoint to the Orc javelin team. Spend 10 gp on a 15 lbs. chunk of iron...or just go and find a rock to throw.
5) Musical Instrument Bayonets: Presented in Song and Silence, and instantly ludicrous to anybody who has actually used a real musical instrument. If you want to destroy your instrument in combat, just whack somebody with it.
6) Scorpion Claws: This weapon from Sandstorm is exactly what it sounds like...monstrous scorpion claws you wear on your hands. Besides making it rather difficult to scratch an itch, I can't help but mentally hear the "crab people" theme from South Park running in the background.
7) Caber: If I recall correctly, this was offered in Masters of the Wild. It was a log that you throw at people. I never understood why this counted as a weapon rather than as improvised use of scenery.
8) Two-Bladed Sword: This weapon led directly to one of the oddest miniatures from WotC, a man in full plate armor wielding one of these. That would probably be the only way to wield one without slicing off your fingers, come to think of it.
9) Spike Shooter: This appeared in Races of Faerun. Any weapon with a spike on the end could be set to launch it as a spring-loaded surprise. Possibly inspired by giant robot anime, I don't understand how you could avoid accidentally shooting it off whenever you swung your battle axe.
10) Icechucker: Ah, here we have a crossbow designed to fire icicles. Oh, and it can fire javelins too, if you actually want to use something balanced and aerodynamic.
Bonus) Vulcanian Thunder Club: This was originally printed in Dragon #304, and it made it into Paizo's Best of Dragon Compendium. While I like the book, I am less enamored with the idea of a greatclub filled with alchemist's fire and shot. It is never explained how you can set it off with the pull of a string, but not by whacking it against your foe (possibly inadvertantly).
There are a few more that come to mind, but 10+1 will do.
Mercurial swords are a thing that has existed in the real world. They weren't terribly effective. The idea was to have the weight back at the hilt end when en garde, but out towards the forte when swung. The mercury channel was hard to forge, introduced a lot of weaknesses, and are a historical footnote.
Two bladed swords also existed... in the poorly documented (but still, documented) post-crusade forms of the Madu - a short-sword/long knife sticking up from and down from a conjoined hilt which also carries a shield, usually a round or small oval. The Madu doesn't require much armor to be used effectively.It's mostly a parrying weapon - it can parry for as much of the body as a full-sized heater can block, but at half (or less) the mass, and adding the stabbing potential both front and back. Note that the African and Indian original versions usually used horns, not swords, and could have more than one in each direction. It may have been parallel development in those two locations.
Shotput vs Rock: Rock: 2 to 3 kg per liter. Iron ball 6 to 7.8 kg per liter. Penetration and bone breaking are about energy density per unit area; a round rock has about twice the contact area of the same weight iron ball, which also means a lot less real world chance to break bones with that stone. also note... at roughtly 3x the density, the diameter of the iron ball is roughly 70% that of the rock. Plus, that ball is known to everyone but orcs as a cannonball.
Most of the rest? Yeah... that said, a long socket bayonet could be drilled out for use as a fife...
Also, the military instruments of most of history are...
Straight Trumpets (going back <3000 years), later, bugles (literally just a trumpet in an oval) and other curved tube trumpets, sackbut/trombone, coach horn
Horn trumpets from just about every kind of horned beast's horn as far back as recorded history goes. (The shofar wasn't
just a religious implement)
Fifes (which are, largely, just a tube with finger holes; if its got keys, it's a piccolo, not a fife) in 6 to 18 inch versions. Bone, Wood, cast metal, rolled metal. Some were mixed media. I've gotten to play a horn-jointed ebony fife with copper inset rings
Whistles (recorders, tin whistles, bone whistles), and bowl-whistles (including the bosun's/boatswain's whistle)
Drums - simple toms and congas, later snare drums, and carried tenor, bass, and great base drums. Marching congas are a real thing, but damned hard on the wrist on the side it hangs on.
Later medieval, we get the tone bells - which are a standard of marching bands still. (barred percussion)
Nothing with valves until the renaissance. Some tumpets/horns had tuning slides; I forget when the trumpets became rounded into the coach horn style, but it was early; proper "oval" trumpets allowed for crooks/slides to adjust tuning, and then the sackbut developed its tuning crook into a proper slide, allowing total pitch control. (Technically, it's not a trombone unless it has a valve with at least once crook, but the distinction isn't made much except by historians.)
Fifes, whistles, drums and trumpets were in fact used on the field for signalling from the earliest days up to WW I, and used occasionally in WW II.
Of those military instruments, the fife could actually make for a decent bayonet... provided it's a socket bayonet. Just drill the tone and finger holes into the socket... be a bit heavy, but reasonable.
A trumpet could be used as an improvised spear, provided the mouthcup is separate... the end can do some real damage. As long as you don't crimp the tube, a bent or dented trumpet still plays reasonably well. (I've repaired a few dozen... it takes a serious ding to impact the sound in any but the tiniest ways in the main register.)
