Kenny Zaron

This plugin allows for network administrators on WordPress multisite environments to send an email to users that 
they select based on the users’ roles in individual sites. For example, checking only “editors” will go through 
each active site and add anyone with the role of “editor” to your list of emails to send to.
To use the plugin after installation & activation, find Users / Mass Email in the network admin dashboard in your 
multisite install. Then, select the user types you wish to email and click on the button for “Load the List”. This 
will load the list of users to email. Then you may compose your email in the boxes provided and click the send 
button at the bottom of the screen. If all goes well you will be presented with a confirmation page indicating 
that your email was sent successfully.
This plugin is NOT intended for administrators to be sending unsolicited spam to their users. In fact, it was 
created with more formal environments in mind. One example would be a University setting where administrators 
of the network may need to notify students and faculty of potential downtime. With the plugin’s implementation 
I would imagine it would be a highly inefficient way of sending spam anyway.

Network Mass Email

Allows network admins to send a manually created notification email to all registered users based on user role.

mikio3

This plugin allows a sidebar to be shared between blogs on a multisite. 
It’s very simple to use.
<ol>
<li>
Use the “Multisite Shared Sidebar” widget to display a sidebar from another participating sites.
<ul>
<li>Specifies the “Blog ID” or “Blog Path”. ( Blog ID: 1,2,3… || Blog Path: ‘path’ or ‘/path/’ )</li>
<li>Specifies the “Sidebar ID”. ( Sidebar ID: ‘sidebar-1’ etc) 
※ Sidebar ID check in a theme file “functions.php”, etc. </li>
<li>“Using current sidebar defined” use it, if you check the check box. (Default)</li>
<li>If you check the “Advanced sidebar configuration” you can customize sidebar defined. 
※ Customizable is ‘before_widget’ , ‘after_widget’ , ‘before_title’ and ‘after_title’. 
※ Details of the parameters see register_sidebar() document.</li>
</ul>
</li>
<li>
Use the shortcode “[shared_sidebar blog=’blog-id’ index=’sidebar-id’ ]” to display a sidebar in the text region.
<ul>
<li>Please write shortcode on a single line.</li>
<li>To the blog attribute specifies “Blog ID” or “Blog Path”.</li>
<li>To the index attribute specifies the “Sidebar ID”.</li>
<li>You can customize the sidebar defined, if you specify ‘advanced_config’ to “sidebar_config” attribute. 
※ [shared_sidebar blog=’blog-id’ index=’sidebar-id’ sidebar_config=’advanced_config’ ] 
   Customizable attribute: ( ) 
      before_widget=” 
      after_widget=” 
      before_title=” 
      after_title=” 
※ Details of the parameters see register_sidebar() document. </li>
</ul>
</li>
</ol>
You can also use this plugin to add sidebars that you have added to the theme yourself.
Beware, however, that after activating the plugin, you must view the dashboard of all of subdomains in the multisite before you can use the sidebar.
<h4>[Setup steps]</h4>
Mr. mkormendy clearly wrote the setup step. 
Mr. mkormendy, thank you very much.
<ol>
<li>in your multisite Network Admin, visit your list of sites, hover over the name of the PRIMARY site that you want to mirror a sidebar of widgets from, and note the id number at the end of the URL for that site within the your multisite wordpress installation</li>
<li>
on your PRIMARY site, create a bunch of widgets in a sidebar (these will all be shared together as a group in the cloned sidebar on a SECONDARY site eventually)
</li>
<li>
in your theme files, where the sidebars are generated, note the id of the sidebar that you are attempting to clone
</li>
<li>
on your SECONDARY site, in your admin widgets section, drag and drop the [Multisite Shared Sidebar] widget to one of your sidebars available on your secondary site (if you use the same theme, you would place it in the same sidebar location as found on the primary site)
</li>
<li>
in the field with the title “Blog ID: or Blog Path:”, enter that ID number that you noted for the PRIMARY site in step 1.
</li>
<li>
in the field with the title “Sidebar ID:”, enter the name of the sidebar that you noted in step 3
</li>
<li>
save the widget, and load up the page of the SECONDARY site where the sidebar exists
</li>
</ol>
You should see the PRIMARY sidebar duplicated inside the sidebar location of the SECONDARY site where you put the Multisite Shared Sidebar widget.
<h4>☆ For Japanese users ☆</h4>
このプラグインはマルチサイトのブログ間でサイドバーを共有します。 
使い方はとても簡単です。
<ol>
<li>
「Multisite Shared Sidebar」ウィジェットを使用して、別の参加サイトのサイドバーを表示します。
<ul>
<li>“Blog ID” または “Blog Path” を指定します。 ( Blog ID: 1,2,3… || Blog Path: ‘path’ または ‘/path/’ )</li>
<li>“sidebar id”を指定します。 ( sidebar id: ‘sidebar-1’ など) 
※ サイドバーIDはテーマファイル内の ”functions.php” などを調べてください。</li>
<li>”現在のサイドバー定義を使用”チェックボックスをチェックすれば、それを使用します。 （デフォルト）</li>
<li>”高度なサイドバー設定”をチェックすればサイドバー定義をカスタマイズ出来ます。 
※ カスタマイズ可能なのは、 ‘before_widget’ , ‘after_widget’ , ‘before_title’ と ‘after_title’ です。 
※ パラメーターの詳細 register_sidebar() のドキュメントを参照してください。</li>
</ul>
</li>
<li>
ショートコード “[shared_sidebar blog=’blog-id’ index=’sidebar-id’ ]” を使ってテキスト領域内へ表示できます.
<ul>
<li>1行でショートコードを書いてください。</li>
<li>blog属性へ ‘Blog ID’ または ‘Blog Path’ を指定します。</li>
<li>index属性へ ‘Sidebar ID’ を指定します。</li>
<li>“sidebar_config” 属性に ‘advanced_config’ を指定すれば、サイドバー定義をカスタマイズ出来ます。 
※ [shared_sidebar blog=’blog-id’ index=’sidebar-id’ sidebar_config=’advanced_config’ ] 
   カスタマイズ可能な属性: 
      before_widget=” 
      after_widget=” 
      before_title=” 
      after_title=” 
※ パラメーターの詳細 register_sidebar() のドキュメントを参照してください。</li>
</ul>
</li>
</ol>
そして、このプラグインは貴方がテーマに追加したサイドバーも共有することができます。
ただし、プラグインを activate した後、使用する前に全ての参加サイトのダッシュボードを１回は表示しなければなりません。
<h4>[お願い]</h4>
<ul>
<li>本プラグインへの投票をお願いします。 </li>
<li>問題点やコメントなどは <a href="https://ja.forums.wordpress.org/topic/144488" rel="nofollow ugc">WordPress フォーラム</a> へお願いします。</li>
</ul>

Multisite Shared Sidebar

Great plugin, which really solves an issue.

Usability could be better (for instance autocompletion/select box for sites and sidebars)
Also some dynamic widgets doesn't work, but that is okay.

Thanks,

Adrian

Solves a problem...

This plugin allows a sidebar to be shared between blogs on a multisite.

Network Mass Email vs Multisite Shared Sidebar