The API is from ZenFire, you have to contact them.
I personally started hating ninja yesterday

Could not get a SIMPLE strategy working for a whole day, and no way to debug.
Their API is availavble in .NET and C++. it is relatively pure, but a dll - i.e. no ui etc. but they do a lot of stuff in it, and no source is available. For the C# part that I use it is:
* 2 dll's
* 3 certificates that you have to point the API to
* compiled 32 bit (sadly, will have to check to get a 64 bit version).
It is not optimal that way - I would like ONE dll, no cert files lying around (integrate them if you have to as resources) and the API could be a little more complete, but in general it is good.
What I miss most is a way to get symbols. No symbol list through the API.
The API also handles trades, or you go with a FIX based API for that (the brokers they have support that).
No historical data either
I will get ninja to get access to their historical data (not so much money there) but otherwise... that is what I plan to use and am implementing right now.