Seeking a GIS for indoor mapping and direction finding

For routing you'll need a vector-line network dataset with nodes at each possible endpoint of a journey. Think of it like a skeleton line running down each corridor with a dot (node) at each door.

It seems you then need one of these for each floor of each building.

You can then use pgrouting in PostGIS or igraph in R to compute routes between nodes. These routes can be overlaid on a more pictorial view of the floor.

To get descriptions ("turn left from elevator, go along 10m, turn right through fire door, go left 10m, you will have arrived at Fred's Office") is much harder. All I can find is this nascent project: http://sourceforge.net/projects/opengraphrouter/ and a few mentions on other StackExchange questions and PostGIS mailing list posts/

This looks cool: http://www.ridethecity.com/nyc?rid=866162

This looks even more immensely cool, and shows how to add the network data to your pictures:

http://www.paulcouch.com/index.php/component/content/article/47-indoor-gis?start=8

They've used Autocad to do that step, but I think their end-user system is open source. Just got to pick my jaw off the floor and read on...

I think the keywords you're looking for are "indoor wayfinding." Here is a product that claims to do just that http://www.here2theresoftware.com/

They use a university as an example: http://www.here2theresoftware.com/Education.html