The Charlotte manga illustrated by Shin Ikezawa and Yu Tsurusaki has concluded with the final volume releasing on January 26, 2019. The manga ran for about three and a half years. Physical volumes are available at Amazon. You can also check any E-manga sites you’re familiar with: Book Walker, Cmoa, Rakuten; some of those also offer physical copies.
The story’s generally the same as the original anime with some minor changes here and there, and there’s content added to the more lighthearted first half of the story. For example, Episode 7–which started the heavier part of the story–is now at the start of volume 5, so that part is now a third of the story instead of half.
Will we see any more Charlotte content in the future, or is this the end of the franchise? Time will tell.