Excel Spreadsheets and VBA Macros

I've found Excel to be a remarkably powerful and flexible tool for data manipulation.

Excel comes with a built-in programming language called VBA that can automate most things that you would use Excel for and some that you wouldn't.
Some examples of where I've found this useful:

• Soliciting user input
• Formatting financial reports
• Prototyping data integration
• Creating portfolio tools that look up stock prices and mark to market

I once wrote a billing system in Excel VBA. Excel created PDFs and emailed them out as well as generating files for accounting and credit card billing. Excel is not the right tool for a real system, but it can get a prototype up and running quickly.

These days I mainly use Python for data manipulation though I've played with Octave for machine learning and Go for faster compiled programs.

Just for fun, here is a Sudoku Solver that I wrote in Excel VBA.