Spacemacs includes Projectile for handling projects. It's extremely useful and feature-rich.
Create an empty text file (in Spacemacs, Notepad++, etc.). Save it as .projectile in your project directory:
By default, Projectile will look for certain directories (such as a .git directory) to determine where a project resides. Creating a .projectile file does it as well.
Next: How to edit your recent projects list in Spacemacs