Well that kind of helps explain it a bit. Speeds up the coding process because you are not starting from scratch but are instead working from a prebuilt framework. Less portability though, I would assume?
Exactly, it takes only minutes, and only a little bit of knowledge, in order to set up ClickBoxer or a new interface like it. Other things obviously would take more work and knowledge, but these programs can be as simple or as complex as anyone wants. If you want to set up round-robin key distribution, Inner Space provides everything you need in order to do it. If you want to set up Picture-in-Picture, Inner Space provides everything you need in order to do it. There is no figuring out how to get your application to run with World of Warcraft or other games, because the platform is already available.

As far as portability, applications would only run under Inner Space. I believe that is what you were asking, but for more information: Inner Space runs in Linux (via Wine or Cedega, etc), and people have had varied degrees of success using it on MacOS X with the same or similar software (or by using Parallels). There are some bugs in the Wine Direct3D implementation, but last time I went to the Wine community to provide information, they tried to tell me I should just write my application native for Linux instead (no thanks). And Inner Space runs on Windows XP SP2 or later (Vista, Server 2008, etc) 32 or 64-bit.