Amongst rumors of the impending arrival of the Apple Tablet, Amazon announced this week that they’re opening the Kindle, their famous e-reader, to external application developers. Techcrunch is not impressed and says “If you are going to try to steal Apple’s thunder just before its big Tablet announcement, you are going to have to do a little bit better than E-Ink Sudoku” but a lot of people are drinking the Apple kool-aid before even seeing a product…

As for the size of the installed base, Mitch Ratcliffe at ZDNet thinks Amazon has sold approximately 1.5 million Kindles so far.

What it means: I think it’s important news. When new “platforms” open up to developers, it’s the first ones in that get the biggest bang for their development efforts. I would suggest to everyone currently involved in mobile applications to sign up for the Kindle dev kit. There are probably interesting hybrid print/online applications that can be deployed on the Kindle (I’m looking at you directory publishers…). You can sign up for the development kit here.