I have spent some time today with two (free!) online applications that are fun to use and work well both on the Windows and Apple operating systems.
The first is ThinkFreeOffice, a Java-based office suite that has a version which allows you to create word processing documents, spreadsheets, and presentations online! You are allocated 30MB of online storage space, you can easily edit a presentation created with Microsoft Office applications, and ThinkFreeOffice allows you to "save as PDF", too!
Think Free Office Online: http://online.thinkfree.com/index.jsp
The other, mycardmaker, requires the Flash plug-in, but it is easy to create you own greeting cards with their beautiful designs or by using a picture or photo from your own computer.