There are many "open source", i.e. free, software applications produced and distributed by service-minded people for our benefit .

1. CutePDF Writer is a free pdf viewer, similar to Adobe Reader. After installation, it appears on your printer list when you try to print a document. This lets you produce pdf versions of documents. CutePDF Pro is a reasonably priced full featured pdf editor, very affordable .
2. MathGV is a graphing utility very similar to handheld graphing calculators, free and in many ways easier to use.
3. PortableApps.com is an extensive with many computer applications compressed and slightly modified (with proper respect to copyright laws) so we can install them on a flashdrive for portability. No modifications are required in a computer's registry, so these applications can be run on secured computers such as those in CF's math labs or a public library. You can download the platform only and use selected apps. The Standard Suite includes OpenOffice, similar to other office suites including a word processor, spreadsheet, database and presentation programs.
4. wxMaxima is a full computer "algebra" and 3D graphing utility. It has a portable version available through PortableApps.com. In common usage, computer "algebra" system has come to include formal differentiation and integration as done in calculus (single- and multi-variable) as well as solving differential equations.