Free office suite – the evolution of OpenOffice. Compatible with Microsoft .doc, .docx, .xls, .xlsx, .ppt, .pptx. Updated regularly, community powered.
Man I hope that is just a me-issue, but I work with excel a lot for work and try to use libre office at home. And the excel alternative is not great. I can see the similarities to excel, but when I want to use it, I have a lot of trouble finding things and using them as I am used to.
You WILL be able to do basic things and I am sure it will almost always be possible to get to similar results, but the way there does not feel the same.