Microsoft Office Excel - Microsoft Office Excel is a commercial spreadsheet application.
MacDown - MacDown is an open source Markdown editor for OS X, released under the MIT License.
LibreOffice - Calc - LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.
Frost - An open API for Blockchain timestamping
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
Typora - A minimal Markdown reading & writing app.