As a Roblox developer, it is currently impossible to add comments to objects inside of the Explorer window. Sometimes - especially if you have a lot of objects inside of your hierarchy - it can be difficult to remember exactly what that particular Frame is responsible for inside of a ScreenGui, or anything of the like.
Sure, you can name the object something that will help you remember, like “HealthBar”, or “Notification”, but sometimes it would be nice to have a tooltip, or another commenting system for objects. I believe other engines like Unreal have this in place - a “tooltip” in the properties of the object, which is simply used for comments on that particular object.
A nice solution would be exactly that, a property of the object labeled “Tooltip” or “Comment” which allows for string input (perhaps rich text), but has no other functionality other than comments. This could be useful for any GuiObject, BasePart, Model, or even Folder.