Jem Vs Darci
A fashion doll from the 1970's I know very little about her except that Jem has "borrowed" a few things from her.  Most notably the face molds.  It is also probably significant to mention here that Jem and Darci did have the same sculptor (more than one sculptor did the faces, however...)

For much more information on Darci, please visit Darci's Very Own Website

Thanks to Rick (BATGIRL), Dave (Dana and Darci photos) & Matt (Erica photo) for their help on this page!
The "Dana" face mold  looks a whole lot like the one used for Roxy, Kimber and Video
The "Erica" face mold adapted for use on Danse, Jetta and Clash. 
Aja's face (left), Darci's face (right).  Not exactly the same, but close.
Their bodies are also similar, they could wear the same shoes (Darci mostly had open toed heeled sandals, I think I've seen some, they are like slides, don't have a back part on the heel from what I recall though I could be wrong.).  I've also heard that Jem's stands were based on those of Darci.  Due to their similarities, I've heard on more than one occasion of Darci dolls (heads particularly) being used for customized Jem dolls.
Well here they are, side by side.  (I think it's obvious who is who, but just in case, Darci is to the left, Kimber to the right).  I've made a chart of their differences below and gave them my own subjective ratings just for fun.
Traits Jem Dolls Darci Dolls Edge
Identity Rock Star/executive from the '80's Fashion model from the '70's Draw
Hair Wild in colour and style Blonde side ponytail, Farrah hair. Jem
Height 12.5" 12.5" Draw
Feet Slightly smaller and daintier looking than Darci's, less arched.  Gross flaps of vinyl in the holes in the bottom of her feet. Jem
Skin Tone Generally are paler than Darci dolls, throughout all races. Can you say "Tan-O-Matic?" (in case of caucasian dolls) We don't judge dolls by their skin colour here! Draw.
Posture Good. My Darci slouches (I'm told this is related to her waist elastic being broken... so perhaps Jems will slouch too in the future :( Jem
Chest size The Starlight girls have bigger breasts than Jem and her friends. Strapless clothes fall down easily. Hardly Barbie, but cup sizes larger than Jem.  Darci (she wears clothes better)
Knees Nice indented knees. Her knees are kind of undefined. Jem
Butt Jem's is quite noticeably larger and rounded. Darci doesn't have that "ridge" that sticks out from the pelvis joint sides that makes an ugly line in clothes. Draw, cuz Jem's butt just looks nicer.
Legs Jem's seams are usually pretty obvious.  Legs don't close together as well.  But they are really nicely sculpted. Smoother, but less shapely.  Ankles "touch" each other. Draw
Belly Button Jem has one. Darci doesn't have one. Jem
Hands Practically the same.  But Jem has fingernails. More obvious "seams" Jem
Torso Nicely defined shoulders and neck. Not well defined. Jem
Make Up More realistic eyebrows. Wild colours that vary from flattering to pretty clown-like. (Yellow blush?) There's something to be said for the natural look.  Very fake looking eyebrows though. hmmm.... still have to say Jem wins.
Ears Apparently doesn't need an ear canal.  Kinda gross looking, actually! (though, if you look at all your Jem dolls, you will notice different ears on all the different face molds) Not much better, but is defined slightly better.  Darci
Articulation Almost identical to Darci, but Darci can easily do lateral splits. Darci
TOTAL 21 points 11 points Jem wins. Surprise!
In the Final Analysis;
Basically, Jem is a souped-up version of Darci, better defined, etc.  Jem mostly loses points because of her pelvis, which, though I think looks more shapely and feminine, restricts her flexibility and tends to make her stand with her legs apart.  I don't know enough about Darci to get into things like wardrobe and personality and such.