GTD in Roam
Roam is a great note taking app where each note page tracks its linked and unlinked references. Even without explicitly linking pages Roam will create connections and help you manage your disparate thoughts. When I was reading through the Welcome to Roam documentation I came across notes on how to setup Getting Things Done in Roam. It was a good starting point but it doesn't use GTD Contexts to narrow down Next Actions and relies a lot on drag-and-drop to move actions around.