Numi - Numi is a beautiful text calculator for Mac.
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.
Observable HQ - Interactive code examples/posts
PCalc - PCalc is the powerful choice for scientists, engineers, students, programmers, or indeed anybody...
iodide - Interactive, notebook programming environment for the web.