How does multisite affect other plugins?

Hello, I've implemented multisite on my site, to enable multi-vendor support for MarketPress. Things went well.
But my website is not an exclusive marketplace. It also has a blog, forum etc included. So I decided to add some of your plugins like chat, Q&A etc.
Now that I think about it, I fear that each of these subsites will have their own exclusive versions of Chat and Q&A. Is it so? Or do these have global support and share the same database across all the multisites?
Hope my question is clear. Please advice!