In reply to Panta's questions regarding these various systems, here are the ones I can answer and that have not yet been answered by others:
Yoroidoshijutsu: The yoroi-doshi is a long, pointy dagger whose name literally means 'armour-piercer' and was built expressly for that purpose. This is essentially a subset of yawara-gi - a catch-all term for fighting bare-handed or with small weapons like daggers - that involves a lot of jujutsu-type techniques to take down or immobilise an opponent, lift up his skirt and poke him very, very hard and deep with the dagger...rather homoerotic in a way, really
Kaikenjutsu: I'm not familiar with all the details, but the kaiken was a dagger similar to an aikucchi (dagger without hilt-guard) associated with the female samurai, so this would presumably be an art of the dagger popular with the ladies. Anyone know how it might be different from tanto/aikucchi-jutsu?
Kabutowarijutsu: This is a bit of a mystery to me - as far as I know, the kabutowari is the seam between the two halves of the main shell of a Japanese helmet and runs along the centreline of the head. Many styles of battlefield kenjutsu have a 'pear-splitting cut' that aims to cut through this weakness in the head armour. Does anyone know if this refers to a weapon somehow related to this phenomenon or if it's just some maniac's expansion on 10 Ways to Split A Man's Head Down the Middle?
Jittejutsu: 'Jitte' can be an alternative pronunciation for 'jutte', but a 'jitte' was also a separate weapon entirely, as Hengest once told me. It apparently is essentially the stabbing head of a cross-guarded spear (juji-yari) with a handle wrapped over the tang, making it something like a straight short sword. Apparently, it is employed as a parrying weapon in combat.
Tekkenjutsu: Already mentioned above.
Hojutsu: The traditional art of marksmanship with matchlocks, flintlocks and hand-cannons.
Hojojutsu: The art of arresting, encompassing the use of jujutsu-like techniques and specialised, exotic tools like barbed poles to entangle clothing to subdue unruly people with less than lethal force.
Yabusame: The art of mounted archery.