This is an example application of Wt, a C++ toolkit for developping web applications.

The benefit of Wt's widget approach to web development is the possibility to define self-contained components (such as in this case the Composer widget) which may be instantiated in the same way as basic widgets, despite its internal complexity (such as keeping track of uploaded attachments and asynchronous uploading of file attachments.

The source code (about 1300 lines of commented C++ code) is included in the latest Wt distribution, or can be browsed online