Portable software is class of software which can be entirely run from a portable storage device (e.g. USB pen/thumb drive, memory card, mp3 player) without the need for installation or configuration on the computer being used. There is a long list of software which can be used in this portable way encompassing the entire spectrum from Internet browser to office applications such as word processing, spreadsheets and email.
The RSCs in Scotland have packaged a collection of over 40 free portable assistive software applications, 'AccessApps', and will be piloting there use over the next 2 months. A range of materials for this project have already been developed, including an introductory guide and a number of video tutorials. More information about this project can be found on the RSC Scotland North & East - AccessApps page.
If you are interested in creating your own, or your institutions, customised set of applications there are a number of 'launchers' you can use to package portable software applications. Wikipedia have a comparison of application launcher (the launcher used by AccessApps is Asuite).