Do you have an API, if so is it SOAP or REST?

Yes we do have a REST based API. We have covered the following modules for now. 

Files / folders

Sites

Activities

Users

ISheets ( Partially developed ) 

The rest of the API resources are on our roadmap and will be developed as we move forward. 

We do have a XML API for ISheets which we will upgrade going forward.  

How often are the APIs changed and, more importantly, deprecated?

We are releasing version 1 of our API with Collaborate 3.3. As this is the first version we are not clear as to how often we will need to deprecate the API endpoints. However the way we have architected the API, the intention is to create a new release of the API with each specific major version, and let the older versions of the API inplace. e.g the API endpoints are at a URL of /api/1/<resource name> , with the next release we will release the API as /api/2/<resource name> so the version 1 will stay intact. 

Who will we deal with when we have API issues? What is the SLA (service-level agreement)?

We will follow the same support pattern that we have currently got for Collaborate. As for the SLA we will use the same SLA as our Collaborate service. 

What kind of documentation do you provide for your API?

We have developed a detailed Microsoft word document as the API development guide, which will be release with Collaborate 3.3. I will be working with Mark Salamon to transfer the documentation to our public facing knowledge base as well. 

Which requirements for the OS environment or run time environment does the API have? Does the documentation reflect the limitations?

As the API is a REST based endpoint, there is no OS limitation for a client application to use it. We have not mentioned this in the documentation as this is a very well known fact for a REST based API.