Today's word processor is an excellent collaborative tool. This is particularly true of the most recent version of Word which enhances collaborative capabilities by making files easily shared across the two major computer platforms, Mac and Windows. Files can be shared by exchanging disks or by attaching them to email. The main hardware requirements is enough memory to effectively use these and related programs. New computer purchases should have a minimum of 32 megs of memory and I recommend 64 or even 128.
Memory is cheap and is in high demand by sophisticated new software.
A school should consider a site license for the software so that all users are using the same software and the same version of the software. While most computer users can use a word d processor, to use it collaboratively you need some minimal training in the features built into word that make collaboration easier, such as version control and annotation of a file by inserting and reading comments. In addition, knowing how to attach a file to email and how to retrieve such a file when you receive it by email are important. The second obvious collaborative tool, also enhanced by capabilities of the latest generation of email programs. For writing, I like email because we're dealing with simple text files and so they put no special strain on computer hardware and software.