Update: A much better research is available here.
After little research, i found several JS grid controls to create google docs like Speadsheet UI. For backend functionality one can copy the implementation used in tikiwiki codebase which is opensource. Another backend approach could be to use many columns spatial database table structure (as used in MS Sharepoint lists)
– http://www.extjs.com/deploy/dev/examples/ (GPL)
– http://www.trirand.net/demophp.aspx or http://trirand.com/blog/jqgrid/jqgrid.html
– http://plugins.jquery.com/project/flexigrid or http://code.google.com/p/flexigrid/
Still In dev, I guess …