Are there any portable versions of QGIS?

Updating this answer with links to PortableGIS 5.8:

https://portablegis.xyz/post/get/

Updating this answer with links to PortableGIS 5.6:

I used that portable GIS (which includes QGIS) last week. A couple of tips:

1. The whole portable system lives in directory called usbgis and the batch files expect that to live on the root of whatever drive it is located on. Either put it on the root, or make a junction on the root that points to the actual location.

   This batch file works from any directory level: .\usbgis\apps\qgis2\bin\qgis-ltr.bat

2. It is big, so make sure it goes on a drive with plenty of space.

It is on my to-do list to tease out a QGIS-only version of this for myself, but I haven't had time yet. I will update this answer once I do with a link.

Or not. The bulk of the portable package is QGIS:

You can download a portable version of QGIS 2.6.1 here: http://webgis.arpa.piemonte.it/geoportale/index.php/documentazione/manuali-e-strumenti/accesso-con-qgis/100-quantum-gis-qgis

You can also create your own portable version with these instructions: http://wiki.gfoss.it/index.php/Qgis_Portable

Pages are not in English so run them through a translator if you need to.

There is a portable (zipped) QGIS version made by Sourcepole:

https://sourcepole.ch/produkte/interlis/

and if you want to make a portable QGIS on your own you find instructions here: https://github.com/Frederikssund/Alternativ-QGIS-installation/blob/master/Readme%20-%20english.md

I rollout portable QGIS-versions at my company based on this instructions and it works very well.