Methods for sharing content in sidebar using WordPress Multisite?

I plan to use WordPress Multisite for several sites, one site for each of several products.

On each site, in addition to product-specific info, I want to show short descriptions of the other products in a sidebar.

My initial idea is that each short description in the sidebar could be simply text or an HTML table that would include a clickable image or table cell that would link to another one of the sites.

When I revise a short product description, I want the revision to show up automatically in the sidebars on each of the sites.

What are some ways (or what is the best way) to implement this feature?

I think some possible answers are custom wizards or blog posts in the sidebar, but I am a WordPress beginner, so I look forward to enlightenment.