Written from a psychological (rather than software) perspective, Rashmi Sinha's article Roller Coasters vs. Driver's Seats: Design and the Concept of Situational Control contains some quite interesting considerations that situational software needs to take into account.

Interestingly enough, situational software has far less "situational control" than traditional applications software: it needs to fit seamlessly into a situation that it has no control over, rather than attempting to control the situation itself, which is virtually all other kinds of software will do.

Instead, situational software improves the control the user has over the (real-world) situation, and that's clearly one of its more significant benefits. In that respect, situational software is an "assistive technology" for situations.