With the UCM and the introduction of the Application Server, we no longer need to give money to Bill Gates or the Evil Empire (Microsoft). Then, once that took off, Avaya used that as a base, for Server Edition.
If you are scared that you will need to learn Linux, in order to work on treh UCM/Application Server/Server Edition, then fear no more. Think about it, we just use clients to program things….One-X Portal uses WebAdmin; IP Office uses Manager (or web manager); Voicemail Pro uses a client. SO nothing Linux yet.