Andrew Downie has provided a website that offers many free, portable applications.
The address is: http://www.techdis.ac.uk/getaccessapps
While the description on the site is reasonably self-explanatory, some points are worth highlighting:
1. All of the AccessApps software is free
2. It all can be run from a thumb drive and does not require installation onto the host computer
The available software covers a wide range of disabilities. As they point out, some people will require more powerful (paid for) software, but this can be a good way of getting started. Something worth keeping in mind is that downloading the complete set of apps can take a considerable length of time.