Luckysheet, an open-source spreadsheet
I still cannot wrap my head around why so many folks want to use such applications in a web browser.For me, web browser applications never reach the responsiveness and ease of use of well crafted desktop applications written in any decent systems programming language or even interpreted languages (not speaking of Javascript).  Maybe I am getting old, but having the browser as a platform for programs is huge setback for many criteria that I personally value.For example, as a free Excel alternative, I fall back to Gnumeric (http://www.gnumeric.org/) from time to time.