DistBear is an Excel spreadsheet to calculate the distance and bearing between two grid squares. It is designed to take its input as maidenhead grid squares, but by over-typing the formulas in the lat lon columns, it can calculate from values for lat and lon.
It was done with Microsoft Excel 97, but as far as I know, it works with newer versions.
I wrote Visual Basic macro functions to do the conversions and calculations. I have provided a bas file with these macros that could be imported into a new Excel spreadheet if someone wants to use them for other purposes.
Read the txt file in the zip for more details.
The spreadsheet is freeware and may be shared in its zipfile form.
Read the text file included in the zip for info about the spreadsheet.