Sure, it's possible, but not without some work. How much work is involved depends on the software you're using. Look at the documentation for each of the applications you use to see if they can be integrated with other software. Wordpress, for example, can share a user database with MediaWiki by using the AuthPress extension for MediaWiki.
Aside from that, the best place to look would be the communities (forums, etc) around the software you're using (if any).
If you want useful replies, ask smart questions.