Unity in-editor to-do list, attached as a component and uses a custom inspector based on ReorderableList. Also see branches for ScriptableObject / cross-scene reference version.
Plans to include a ScriptableObject version of the To Do list, so it doesn't need to be on a GameObject / in scene. Currently you can use a prefab to kinda do this, but this would be a cleaner solution.
The only problem is you won't be able to link Scene GameObjects/Components as Unity can't handle references to scene objects outside of the scene itself (as far as I'm aware at least, and it also can't do cross-scene references). Don't really want dependency on some external GUID system... so basically wrote one myself. See #3.