1. It's based off manga series.
Gunnm was first published in English as Battle Angel Alita by VIZ Media in comic book format July 1992 to March 1998. It was also republished under the VIZ Graphic Novels imprint from July 6, 1995 to December 6, 1998. Authors were Kishiro, Yukito (Story / Art).
2. There was a short anime that adapted the manga
It was published as anime ( OVA, 2 Episodes) from Jun 21, 1993 to Aug 21, 1993.
3. Alita: Battle Angel - 122 minute-long film
The film is longer from its anime (2 Episodes, OVA)
4. The manga was also adapted into a video game for the PlayStation.
Kishiro was not being satisifed with the ending of the original Battle Angel Alita so he has created an action role video game for the PlayStation based on the Battle Angel Alita manga series. The game was published in 1998. Many people played the game in the PlayStation.
5. It’s also set in the future
One of the things that are very cricual for the story is that it's set in the future. Most manga is either set in present day or in the past days so when you find one that is set in the future, this can make it stand out right from the start. The most interesting side of this movie which is adopted from an anime can be that it's set in the future.
6. Nine volumes of material available
The last fact that you need to know about Alita: Battle Angel is that nine volumes of material are currently available from which things could be adopted. That's good news for fans that will wait for the future movies from this manga.