If your project includes a custom written software application, there are several type of specialized writing skills that are applicable to the project. First, the project needs a set of software specifications, in much the same way that a custom built home needs a set of specifications and drawings. Thorough specifications are also critical to the bid process. User's manuals, and possibly a technical manual, allow your users to quickly gain understanding of the software concept and flow. On-line help functionality will allow your users to explore features in-depth.