I was looking for information on how to run a Skype for Business 2015 trusted application on a standalone (aka workgroup joined) server. The need is for development reasons only: my dev workstation is in a workgroup and I cannot join it to the domain running the Skype infrastructure. I believe I read somewhere that this should be possible but my attempt to find an article/blog post describing any required steps to make it work failed.
It's possible, you just need to follow the same instructions as a normal domain joined machines. I would only setup for a manually provisioned application as a auto provisioned application requires your machine to setup to replicate the topology. (This can be done, but is not nice - you can follow the Edge server setup as a example of this type of setup on a non-domain joined machine).
You machine needs to setup as a application pool within the SfB topology.
For a non-domain joined machine you will most likely have to install the required certificates mainly.
You will need to install the CA certificate for the domain that SfB uses into your machines trusted root and you will also need to get the domain to generate a certificate for you machine and install it into your certificate store so that your UCMA application to select and use it in the UCMA setup.
Once your machine is setup as a application pool with the required certificates. Then you just need to setup the trusted application within the SfB topology.
All of this is just easier with a domain joined machine as you can only do a lot of these steps on a domain joined machine (or on the SfB server itself).
Once the SfB topology is setup then developing the UCMA application on your machine it possible.