How to send notification like below?

[ZunerDev (Zuner)]

[CMVProduction (CMV)]

There are various ways. You can use the Message and Hint objects, or just create a gui.

local m = Instance.new('Message')
m.Text = "Sample Text"
m.Parent = workspace

or

local m = Instance.new('Hint')
m.Text = "Sample Text"
m.Parent = workspace

These two objects are deprecated so I would suggest you create your own GUI using a textlabel.