Caelum

Caelum the "Chisel" is a Celestial Spirit that can transform between three things for it's master Angel. Apparently it is only an item and not a sentient being.

Oracion Seis arc
Caelum is summoned to do battle against Lucy Heartfilia. As it is summoned, it fires a blast at Aries and Loke dispite Aries being on it's side. Gemini then uses Caelum in sword for to attack Lucy but as Gemini refuses to hurt Lucy, Angel takes Caelum to attack herself. In the end though, Caelum is defeated by Lucy.

Forms
1. The Cannon Form: The first form to be used and a therefore a good candidate for it's default form. In this form it appears as high tech cannon that can launch powerful blasts of energy. It can be assumed that Caelum has control over the path in which it fires its beam as it curves it around Lucy to avoid harming her. It can be assumed that Caelm has emotions, since there could be no other reason it would choose to curve the beam.

2. The Flight Form: The second form to be used. It is a another good candidate for Caelum's Default form because in this form it appears as a simple winged sphere which seems to make it the basis for the other forms. This form has yet to be seen using any attacks and it probably has none. Though it's likely this is the only form shown that can move considering it's the only one that looks like it could, but it hasn't been seen doing this yet, so there is no proof of this.

3. The Sword Form: This form has the "Chisel" part of the sphere enlarged so much it looks like the Chisel is the blade of a sword with the Sphere part being it's hilt. This form is in fact the first evidence of some stellar spirits having no ability to resist their masters and it seems Caelum even lacks a personality or speech abilities which makes it very different from other stellar spirits shown so far. The proof while it's wielder Gemini stopped attacking Lucy when it realized Lucy's love of her kind. Caelum still seemed to be under Angel's control as if it couldn't feel Lucy's emotions or if it could didn't feel any emotions of its own; this is, however, assuming that it curved the path on purpose.

Trivia
The modern translation of "Caelum" is usually given as "chisel," which is not quite accurate. If "chisel" were meant, then the constellation should be called "Scalprum." The Chisel has different forms in takes, but none of them have any official names. These names given are just what I think they might be called.
 * "The Chisel" is the modern translation of the constellation Caelum, but apparently that's not quite accurate. The word is ambiguous, in Latin caelum means both "the heavens" and "birin," which is an instrument used for engraving on copper and fine metals. It is this instrument that Lacaille had in mind when he named the constellation.