You do not need Spark itself to create a chat application. Let's say you're making a web browser. While it may be nice to take inspiration from Chromium, it is not necessary, and is an independent product. The same happens here.
Spark is a client for the XMPP protocol, it seems. Making a chat application involves a server and a client. If you are using XMPP there are many clients and many servers out there so you only need to create a server, or a client, or both if you'd like.