Hello,
To answer question 1 - it is an alternative to the Microsoft RemoteApp host that is free, open source and does not require Windows Server to run it. The client tool is still MSTSC on Windows and whichever flavor of RDP you like in Linux/Mac that supports RemoteApp. If you do decide to use this on a Server OS, it is much more lightweight and easier to set up with the drawbacks of having no native failover or clustering or load balancing support.
To answer question 2 - The application is running on the HOST machine, not the client machine, so as long as you are licensed to run it on the host (need a remote desktop license (RDS CAL) and a license to the application being run), you are in compliance. Since the host is not a server OS, you should not need an RDS CAL, but that is probably a better question for Microsoft than a random forum. If Microsoft decided to audit you and found you out of compliance, citing a random post on the internet won't get you out of hot water.
Thanks,
Brian