Popclip - PopClip appears when you select text with your mouse on your Mac.
Numi App - Numi is a beautiful text calculator for Mac.
Pantherbar - Pantherbar is a tool that lets you perform instant actions when selecting text.
Soulver - Soulver is a software application that functions as a calculator that allows you type a continuous stream of information rather than having to input data into multiple cells.
Universal Tip - Programmable tooltip that can be used with every macOS app
Soulver 3 for Mac - A smart notepad with a built in calculator