|You might also want to take a look at Libre Office, which is a spinoff from Open Office, created by some members of the team that originally worked on Open Office. |
Quick history lesson - Open Office was originally developed by a German company and acquired by Sun Microsystems to be an in-house alternative to Microsoft Office. Sun then released it to the public about a year later as a free open-source alternative to Microsoft Office. Sun was later acquired by Oracle, which in 2011 discontinued development on Open Office, fired the development team, and donated the project to Apache Software, its current owner. Apache has done very little additional development; the latest version was released in 2016.
Some members of the development team regrouped and started developing Libre Office, using the open-source code as a jumping off point. Libre Office is still being developed and the latest version was released last year.
I've used both, and I prefer Libre Office because a) it feels like more thought went into it, and b) it's still being actively supported. Both are virtually MS Office clones, both handle just about any file format you can throw at them, and both are totally free.