If a user tries to open a Workbook that is already open, then they normally get a message saying that the File is locked by a certain user and would you like to open the file in Read only mode. However, you can open a workbook in shared mode by following these steps. First open the file that you want to share, then once the workbook is open, go to the Tools menu and choose Share Workbook from the drop down menu. The Share Workbook dialog box will now appear. To enable sharing, you simply click once on the Allow Sharing check box, so that it has a tick. Once you do this other people will now be able to use your Excel workbook whilst you are working on it.
In terms of features, NeoOffice (donations accepted) is huge, truly a viable alternative to Microsoft office. It includes all the basic components: Writer, the Word processing component; Calc, for spreadsheets; Impress, the presentation module; draw, for the creation of graphics and diagrams; and Base, the database component. The spreadsheet component has some sophisticated features like Advanced DataPilot technology, Natural language formulas, an Intelligent Sum Button and a comprehensive range of advanced spreadsheet functions.