I am aware of a cassette pencil by Lion and Staedtler. Are/were there others?
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The ones I know of:
Berol Cassette, Cassette XL
Sailor/Sheaffer (the latter called the Ultra Fineline)
Pentel Quick Dock
Parker had a couple of versions whose names Iām blanking on at the moment but I think they may have been part of the Jotter series.
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Oh! And the Pentel Injecto, of course.
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platinum MK-120 (now renamed to 150)
platinum MK-100
uchida microsharp 110
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4 different Injecto
P154
P155
P1004
Q604
The Pentel Quick Dock also came in a couple of different models
QD5
QD5E
QD7E
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Would anyone mind explaining the Pentel Injecto to meā¦?
WHAT is going on with that dude?!? The one that just sold on Yahoo.auctions was sexy as hell (and pricey as hell).
I know it is SOLELY a 0.4mm, and it has a ācartridgeā(of āWHAT??ā, I do not knowā¦)
Any explanation of this enigma will bring a considerable amount of calm to my āWTF?!? IS THIS THING!ā reactions* it often createsā¦
Thank you in advance 
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The cartridge is the lead ācontainerā, think of it as if itās a mechanical pencil + a rechargeable pen. In some cases (STAEDTLER Cassette) the cartridge also came with an eraser, itās a very unique idea that (thankfully) didnāt catch on.
From post in r/mechanicalpencils by Xiao
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What is the point of this?? Did they sell cartridges on their own so you could inter-change? And why a pencil solely devoted to 0.4mm? (Iām not complaining-0.4mm is turning into my favorite- but I donāt see a CEO expecting the least popular lead size being the catalyst to a whole new realm of undiscovered profits in the M.P. Market?
Iām still scratching my head.
Thank you for the info provided thus far 
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The Pentel QD5, QD5E & QD7E all come with erasers. In the case of the QD5E & QD7E, they are Twist Erasers. Also, these 3 can be carried without a cap for the cartridge, which the Injecto required.
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Newman also made one, this is the lower end version. The 1000 yen model is all-metal. Paper Mate made their PACER Cassette model.
Not shown: Sailor also made oneā¦ a very complicated design.
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Stabilo cassetto 3270 seems to be another one P1050747 | Cassette pencils | 2nd_astronaut | Flickr
I refer to the Staedtler case: I think, the idea was indeed to have disposable cartridges, which were separately sold (you donāt need lead containers anymore, so itās no increase of waste). Advantage for the user is, that you donāt have to deal with the dirty and delicate single leads and (with some pencils) that you see how many leads are left thru the window. Advantage for the supplier is, that you are tied to their pencil, if you bought cartridges ā¦ To have an eraser with the cartridge seems to be not a bad idea.
Why Pentel chose 0.4mm: no idea.
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It was kind of a gimmick. But the premise was that you could preload lead of various hardness levels into multiple cassettes and then just swap easily as you needed. No fuss. No mess.
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I have a nice set of Sailor cassettes (all but one or two, I think), but I canāt get ANY of them to work properly after disassembling them.
Considering selling them on this basis alone 
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Bummed to hear that, @pearsonified. When you say disassembled, you mean just unscrewing, removing the cassette and then reinserting it? Or did you disassemble the cassette as well (if itās possible)?
I got one of them a while back in a lot. And I took the cassette out to examine. I put it back in and it worked, but then I noticed a lineā¦ and yeah. the clear plastic had split. The quality of construction didnāt appear to be as good as what PILOT, Pentel, and Platinum normally produce. But it sure looked nice. And I like that idea of a ālead windowā thatās a whole 360 degree segment. Reminds me of some vintage ink pens.
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Iām talking about all the parts from the barrel joint down to the tip. These are pretty well showcased in @drifandās link above.
Canāt figure out how to get it back together; the only explanation that makes sense is that it was originally glued, and now that the glue has dried and cracked, the pencil is unfortunately useless.
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Could be. Maybe someone else here has more experience with them and might have some pointers.
Sailor Cartridge is one of those crazy cool pencils in theory, but lacking in execution. The idea was really interesting - use a cartridge with a plunger at the back so you can switch lead diameters.
The plastic versions are extremely fragile and fall apart even if you look at them wrong. The metal ones are better - Iāve only disassembled the front of one and was able to put it back together fortunately. It was harrowing though.
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Not to hijack this thread butā¦.both @pearsonified and @popossum crawling out from under their rocks on the same day is crazy crazy. Welcome fellas. 
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I had a feeling. Thanks for confirming!