Like other Portable Apps, Portable GIS is a self-contained stack of open source GIS software for Windows, including GRASS, QGIS, FWTools, PostgreSQL/PostGIS, MapServer, Tilecache, Featureserver, GeoServer, and lots more. It takes the pain out of installing and configuring all this software by making it stand-alone – you can upzip it to a thumb drive and run everything from there.
This is a cool concept, and it lets you run lots of software without having to go through the setup processes and extra dump extra garbage to your registry. It also lets you take some GIS tools with you for those occasions when your away from your office.
I’d definitely recommend giving Portable GIS a shot. It’s a big download (450mb+), so plan accordingly.