Sometimes nothing but Microsoft Office will do especially if the content creator intends to share complicated documents for other people to edit. However, for simple (or as complicated as you like!) spreadsheet tasks and word processing documents Libre Office and its sister application Open Office is perfect.
Libre Office is fully featured and offers almost as many features as Microsoft Office but it as it is open source it doesn’t cost anything. This is very useful when the cost of a genuine Office licence can easily be 2/3 of the cost of a new computer.
We often recommend using Libre Office as a replacement for out of date or unlicensed copies of Microsoft Office and for most people it is all they will ever need.
The downside is the interface is a bit different so a small learning covering is required and you will need to remember to save documents in the relevant Microsoft formats if you want to open the documents using older versions of Microsoft office at a later date.
Find out more about the Libre Office project