Often Windows CE, Windows Mobile, and Pocket PC are used interchangeably, in part due to their common origin. This practice is not entirely accurate. Windows CE is a modular/componentized operating system that serves as the foundation of several classes of devices. Some of these modules provide subsets of other components' features (e.g. varying levels of windowing support; DCOM vs COM), others which are separate (bitmap or TrueType font support), and others which add additional features to another component. One can buy a kit (the Platform Builder) which contains all these components and the tools with which to develop a custom platform. Apps such as Excel Mobile (formerly Pocket Excel) are not part of this kit. The older Handheld PC version of Pocket Word and several other older apps are included as samples, however.