The Doom Star, Jedi Killers, and Other Early Changes to Star Wars: The Force Awakens
The crossguard lightsaber was almost a double-bladed two-toned lightsaber
In early designs for Kylo Ren's weapon, it didn't have that now-iconic cross imagery, but rather was a double-bladed red and blue lightsaber, as the designers were playing with the motif of fire and ice.
Starkiller Base was originally called "The Doom Star"
In early concept art, Starkiller base was an Imperial Snow Base built inside the planet of Dantooine and was called "The Doom Star." The base would steal energy from nearby suns, making the entire galaxy darker. It's easy to see why they changed the name, since Doom Star isn't all that different from Death Star, but it's interesting that the nature of the weapon changed so much.
The Resistance developed a super-weapon called the "War Hammer"
General Leia was shown to be developing a super-weapon called the "War Hammer," which would have been several times the size of the Star Destroyer. It would have looked like a huge ship that could penetrate any shield with its front.
The main villain was "Jedi Killer"
Several Big Bads were explored in the early concept art, but one that recurred the most was "Jedi Killer," which greatly resembled the Inquisitors from Star Wars Rebels. Some of the concept art for Force Awakens was ultimately used for Rebels, including a Sith Jedi Killer design that was re-appropriated for the Fifth Brother.
Darth Vader's castle
The unused designs for Vader's castle for Empire Strikes Back were almost used in The Force Awakens. It would have served to obscure General Leia's Resistance base, which would have been located underneath it.
Han Solo was a drunk
Early concept art showed Han Solo a little more down on his luck, with a Western look of a beard, combed-back hair, and a long duster jacket. Rey and Finn were supposed to meet him for the first time on a planet called "Crime City," while he was getting drunk at a seedy bar.
Snoke was a woman
Creative supervisor Neal Scanlan wanted Snoke to be female, and even built a full-size maquette for the character. But ultimately, Andy Serkis was hired for a motion capture performance, so the character was changed.
BB-8 was a probe droid named Surly
As we already know, BB-8 went through several different versions. Rey originally had a small flying droid that would hover beside her, and Poe's droid originally looked like R2's head on an Imperial probe body. Its name was Surly, and we would have met him for the first time in the droid repair of a Star Destroyer where he would have narrowly escaped incineration.
Maz Kanata was a practical effect
They went through many designs of Maz Kanata, most of which looked like wrinklier versions of Yoda. She took the longest to design, only finalized in October 2015, so they ran out of time to build her as a puppet. This is a shame, as I always prefer practical effects over CGI, but Maz ended up cute enough (although not nearly as cute as Yoda).
Rey's original name was Kira
In early concept designs, Rey was a "loner, hothead, gear-head, badass," named Kira. The early story focused on her self-awakening, which makes sense, since Rey's storyline was ultimately the heart of the film.
Finn was a smuggler named Sam
Finn was originally supposed to be a Han Solo type named Sam, a smuggler who screenwriter Michael Arndt described as "pure charisma."
Poe Dameron was almost a Jedi or bounty hunter
Poe Dameron was given the name of "John Doe," which makes sense, since he was originally supposed to die in the crash-landing on Jakku. He was drawn as a black man in his 30s or 40s (while Finn/Sam was drawn as white), and was supposed to be a Jedi or a bounty hunter before they settled on a "Republic military man."
Finn was rescued by an indigenous alien tribe
After the crash-landing on Jakku, Finn was supposed to be rescued by an alien tribe and healed in a ritual in which he is "reborn as a hero." We're glad they didn't go this route, as it's a little cheesy at best and a little "noble savage"-esque at worst.
The map to Luke Skywalker was hidden in the Death Star
In early drafts, Rey found the map to Luke Skywalker while scavenging in the second Death Star, which is now submerged underwater. In later concept art, she takes the Millennium Falcon underwater in order to explore the defunct weapon.