A popular Severus Snape neutral fanfiction is 'Midst the Shadows'. In this story, Snape's actions are examined from a fresh perspective. It shows how his past experiences shaped his actions without making him seem like a simple good or bad character. The story has a lot of depth and the author uses great descriptions to bring out the essence of Snape's character in this neutral context.
There's 'Snape's Alternate Timeline' which is really interesting. It explores what might have happened if Snape had made different choices at certain key points in his life. The author does a good job of keeping his character in a neutral zone, not overly glorifying or villainizing him. This fanfiction also delves into his relationships with other characters like Harry Potter and Dumbledore in new ways.