Heidegger, as a tangent in his discussion of Daesin, talks about objects/tools which can be either ready-to-hand or present-at-hand.
As I find Heidegger painfully unreadable, but his concepts useful, which philosophers discuss these concepts and apply them to the philosophy of technology?
At present, I'm aware of Dreyfus's discussion of the concepts, are there any others?
Heidegger is one of (if not the) most influential philosopher of the twentieth century, so there have been several 'return-to-Heidegger!' sort of movements which really plunged into his metaphysical work. (In particular, this notion of 'instrumentality' or 'tool-being' has received a lot of treatment.)
The philosophers involved with the Linguistic Turn are one very good place to go. Derrida, of course, writes a great deal on Heidegger.
As far as serious contemporary work goes, the object-oriented ontology of Graham Harman utilizes Heidegger extensively, and in particular radicalizes the concept of tool-being. I might suggest starting there, as it's really accessible. Zizek writes a little bit on Heidegger, but again that will be true of any serious thinker of the last century with some exceptions (but not that many.)
According to Wrathall's reading of Heidegger, tools can switch between readiness to hand and presence at hand and that they become present only when they break.
This struck me as having been highlighted in Winograd & Flores's Understanding Computers and Cognition. They talk about the detail revealed by breakdown providing the opportunity for improved understanding and new design.
