Markus Echterhoff

If you have a multisite setup, you normally cannot have the same bbPress forums across all sites of the network. Now you can.
Install this plugin and activate it on the main site and for each subsite that should use the main site’s forums, or network-activate to enable on all sub sites.
If you want both main site and sub site forums displayed on the sub site, set a different root slug and topics slug in the forum settings. After that, both slugs will be known on the sub site and display their respective forums.
BUT! There is a reason why you cannot normally do this and that is because the code base is not really supportive of it. I have monkey patched my way to the goal and I’m doing some evil black magic like hooking ‘query’ and running regular expressions on the query. All of this is only ever done to your forum pages, so be cool, give it a try. If it works for you: great. If it doesn’t: deactivate, relax, look for a different solution (or patch mine).
Profile Note: Profiles are not merged! Favorites, topics started etc show main/sub site only. If you want your users to see all their subscriptions in one place, you’ll have to write some custom code and likely patch my code too.
BuddyPress Note: It does work with network enabled BuddyPress, but they don’t play together nicely because of the BuddyPress/bbPress integration stuff. I have monkey patched this to work. If you do not have BuddyPress installed in /members/ you’ll have to monkey patch my monkey patch, please see the code. And as for the profiles: Same thing as with bbPress profiles.

Multisite bbPress Slave

Make sub sites use the main site's bbPress forums

Freemius

DEV Institute

Joachim Jensen

<h3>Content Aware Sidebars is the #1 WordPress Sidebar Plugin</h3>
You can optimize conversion rates, boost on-site SEO, upsell products, and much more by displaying different widget areas on different conditions.
Create tailored widget areas in seconds. No widget logic coding required.
<h3>Show or Hide Widgets on Any Page (Yes, any)</h3>
Replace your theme sidebars on different conditions, or insert widget areas with shortcodes. The following Display Conditions are available out of the box:
<ul>
<li>Posts, Pages & Custom Post Types</li>
<li>Content with Tags, Categories, or Custom Taxonomies</li>
<li>Content written by select Authors</li>
<li>Page Templates</li>
<li>Blog Page & Post Type Archives</li>
<li>Author Archives</li>
<li>Taxonomy Archives</li>
<li>Front Page, Search Results, 404 Not Found Page</li>
<li>bbPress Profiles, Forums & Topics</li>
<li>BuddyPress Profile Sections</li>
<li>Languages (Polylang, qTranslate X, TranslatePress, Transposh, Weglot, WPML)</li>
<li>Pods Pages</li>
</ul>
<blockquote>
You can even combine conditions in any way you like! E.g. target all posts in a select category and written by a specific author.
</blockquote>
<h3>Add Unlimited Sidebars & Widget Areas</h3>
Create a post sidebar, a page sidebar, a category sidebar, or any custom sidebar you need – no coding required. CAS will never slow down your site, even if you create a lot of custom sidebars and conditions.
<blockquote>
Sidebars – Quick Select© lets you add or select widget areas directly when editing a post or page.
</blockquote>
<h3>Schedule & Disable Custom Sidebars</h3>
In the All-in-one Sidebar Manager you just pick a start and end date for when widget areas should be displayed, and CAS will take care of the rest.
<blockquote>
1-Click Sidebar Activation© lets you activate or deactivate widget areas instantly.
</blockquote>
<h3>The Most User-friendly Widget Manager</h3>
When adding new widgets to sidebars, Live Search will find widgets instantly, and the smart split-screen makes it a joy to manage a lot of widgets and sidebars.
<blockquote>
The Enhanced Widget Manager adds the signature turquoise line to easily identify custom sidebars.
</blockquote>
<h3>Sidebar Plugin Integrations & Support</h3>
CAS autodetects Custom Post Types and Taxonomies created by any plugin or theme. Built-in support for some of the most popular WordPress plugins means that you e.g. can create WooCommerce sidebars for select products or BuddyPress sidebars for your members.
<ul>
<li><a href="https://dev.institute/wordpress-sidebars/bbpress/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">bbPress</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/buddypress/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">BuddyPress / BuddyBoss</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/easy-digital-downloads/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">Easy Digital Downloads</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/multilingual-plugins/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">qTranslate X</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/pods/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">Pods</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/multilingual-plugins/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">Polylang</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/multilingual-plugins/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">TranslatePress</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/multilingual-plugins/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">Transposh Translation Filter</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/woocommerce/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">WooCommerce</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/multilingual-plugins/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">Weglot</a></li>
<li><a href="https://dev.institute/wordpress-sidebars/multilingual-plugins/?utm_source=readme&utm_medium=referral&utm_content=integration&utm_campaign=cas" rel="nofollow ugc">WPML</a></li>
</ul>
<h3>Customize Your Widget Areas Your Way</h3>
Without writing any code, you can modify the HTML and CSS classes of widget areas, widgets, and widget titles. You get full control over the look and feel of your sidebars and widget areas, no matter what theme you use.
<blockquote>
Sidebar Visibility lets you elegantly hide any widget area for logged-out users.
</blockquote>
<h3>Complete control over your WordPress widget areas</h3>
<a href="https://dev.institute/wordpress-sidebars/?utm_source=readme&utm_medium=referral&utm_content=title&utm_campaign=cas" rel="nofollow ugc">Upgrade to Content Aware Sidebars Pro</a> and get these additional powerful features:
<ul>
<li>Totem – Smart Floating Button 
Like the button you may have seen by Intercom or Helpscout, only this is for all your widgets</li>
<li>Sticky Sidebars & Widget Areas 
Make any sidebar or widget area sticky without hurting site performance. No jQuery and no bloat</li>
<li>Widget Areas after Paragraphs 
Display a widget area after a specific number or percentage of paragraphs in your content</li>
<li>Even More Display Conditions
<ul>
<li>Advanced Custom Fields data</li>
<li>Meta Box data</li>
<li>URLs + wildcards</li>
<li>Referrer URLs</li>
<li>Date Archives & Content by publish date</li>
<li>BuddyPress Groups</li>
<li>Random</li>
</ul>
</li>
<li>Widget Area Designer 
Add responsive widget columns and edit colors, backgrounds, paddings, etc.</li>
<li>Widget Areas in Theme Hooks 
Intelligently infuse new widget areas into your theme without coding</li>
<li>Automatic Widgets Backup 
Easily restore any changed or deleted widgets</li>
<li>Widget Cleaner 
Save memory and remove clutter by disabling and removing unused widgets</li>
<li>Extended User Visibility 
Show or hide widget areas for User Roles, BuddyPress Groups, and more</li>
<li>Time & Weekday Schedule 
Display widget areas only in select time ranges on given days</li>
<li>Container Widget 
Turn widget areas into reusable blocks and show the same widgets in different places</li>
<li>Duplicate Widget Areas 
A real time-saver when adding new similar widget areas</li>
<li><a href="https://dev.institute/wordpress-sidebars/pricing/?utm_source=readme&utm_medium=referral&utm_content=more&utm_campaign=cas" rel="nofollow ugc">and so much more…</a></li>
</ul>
Upgrade at anytime instantly and securely from your website’s Admin Dashboard.
<h3>More Information</h3>
<ul>
<li><a href="https://dev.institute/docs/content-aware-sidebars/?utm_source=readme&utm_medium=referral&utm_content=info&utm_campaign=cas" rel="nofollow ugc">Documentation</a></li>
<li><a href="https://github.com/intoxstudio/content-aware-sidebars" rel="nofollow ugc">GitHub</a></li>
<li><a href="https://twitter.com/intoxstudio" rel="nofollow ugc">Twitter</a></li>
</ul>

Content Aware Sidebars – Fastest Widget Area Plugin

Display new sidebars on any post, page, category etc. Works with Classic Widgets, Block Widgets, and all themes!

Multisite bbPress Slave vs Content Aware Sidebars – Fastest Widget Area Plugin