LaTeX is a powerful document preparation system that provides many advantages for people working in Linguistics: automatic numbering of examples, automatic glossing, automatic tree drawing, a full set of mathematical symbols, excellent bibliographic citation and reference formatting. And it's all free and open-source.
Here you'll find some packages that I've written, along with some other software. Except for the MSU Letterhead package, all my packages are available at CTAN (the Comprehensive TeX archive), and are also included in both the TeX Live and MikTeX distributions. If you are already using one of these distributions, and your TeX distribution is up to date, you should probably have the packages installed already. If they are not installed, you should use your distribution's package manager to install them rather than downloading them directly from CTAN.