ThinkFree provides a similar service to Zoho offering free, Web-based Word, Excel and PowerPoint software. I found ThinkFree’s charts matches the features in Excel (and is better than ZohoSheet and NumSum).
In fact, ThinkFree’s compatibility with Microsoft Office is so awesome, at times, it is easy to forget you are not actually using Word/Excel/Powerpoint. I am surprised the use of the small toolbar icons does not constitute not a breach of copyright.
ExtremeTech produced an excellent, comprehensive review of ThinkFree which describes the features in more depth.