LibreOffice

LibreOffice is the best open source office suite. It's able to open all common office files. It is feature rich and stable. The office suite runs on different OS, e.g. Windows, Linux, MacOS.

Would give it 5 stars except for occasional bugs.

As always, compatibility with OOXML files (.docx, .xlsx, .pptx) is the primary hassle of sharing files with non-LibreOffice users; but the compatibility keeps getting better and better. Use PDF export to share, if you don't have to provide editing access. Google Docs plays nice with ODF (thank you, Google!), so you can share that way too.

I only just started using LibreOffice, but it seems to have all the functionality of Microsoft Office. The stock templates may not look as nice, but I could open and edit all of my existing Microsoft Office documents without a problem, even the less typical .dotx files. The formatting was even retained! I use a lot of pivot sheets and was surprised to find that those work well too. I have been using Microsoft Office almost exclusively since the 90s and found that transitioning to LibreOffice was pretty straight forward. I am also looking forward to having a database too since I lost the ability to use Microsoft Access after switching to a Mac. I will start using LibreOffice more often now and will need to get used to having the ability to do word processing, spreadsheets, presentations, graphics and databases all from one app.

I am disappointed to have never used this open source program before. There were no issues with the download and setup on my laptop. It is very easy to use with qualities similar to other proprietary programs of its kind.