Worldbuilding

I suppose it depends on what you consider "interesting" - I tend to find relatively "conventional" sci-fi stuff like coilguns or advanced missiles, so long as they're fairly well designed! But with that in mind, let me discuss a few relatively unique ones:

• C+ Artillery is... exactly what it sounds like. Actually predating FTL travel by a fair bit (humans... go figure), C+ artillery hurls a massive slug through a sequence of faster-than-light spacefolds, like skipping a stone off a pond. The results are utterly catastrophic: Not only does the projectile bypass armor and interceptors as it "skips", but the target is subject to the unspeakable gravitational shear forces at the event horizon of the final fold... and that's before the enormous slug at .99C slams into it. They're used for cracking fortress-stations and dreadnoughts, and thankfully have never been fired against a planet.

• The typical infantry armor can be outfitted with the SPG-22, a 60mm, box-fed semi-automatic coilgun mortar. This system is mounted pointing vertically on the back, and is fed from a 4-round box magazine. It's most notable for the lack of need for emplacement: If necessary, the operator can kneel, the armor braces itself in place, and the mortar fires as necessary. Typically the user is actually aiming the system using an onboard firing computer, while an assistant operator keeps the weapon fed. In this way, rapid firepower can be pushed down to a platoon level.

• The AGS-202 'Easifa' ('Storm') is a monstrous cluster munition: Weighing in at over 3,000kg, it fragments into several individually-guided petals, which in turn try to arrange themselves for maximum coverage of an area... before they in turn disperse a mix of pyrophoric incendiaries, high-explosive fragmentation, and guided armor-penetrating bomblets by the hundreds. They're meant to erase entire defensive lines, although if you can disperse one over a base, the results are equally terrifying.