Horizontal adds a container with up to 100 horizontal blocks of content to Stacks pages.
It allows the addition of as many Horizontals as needed on a page and can be used as a stylish image slider or to display any type of content.

The configurable horizontal scroll bar for webkit browses (Safari and Chrome) has options for colours and image for the scroll thumb.

Horizontal is easy and fun to use, it can display directional arrows that can scroll to any block of content with configurable scroll speed, colour and position.
The stack is not responsive.

Horizontal's features in a glance:

• up to 100 blocks of content
• configurable blocks width and height
• webkit scrollbar options
• directional arrows with positioning
• fade-out arrows on container scroll
• configurable speed and target block
• first block scrolling automatically

Edit: Lucas has reacted to my criticism and has updated Horizontal. It is now responsive.

BLT — British readers will now immediately think of bacon sandwiches. 

However, today it's Brandon Lee Theme Design presenting Vertigo, a brand new, fully responsive theme for desktop and mobile.
Vertigo is a theme loaded with style, modern web features and functionality. Take advantage an animated, user focused navigation menu, 3 responsive slideshow effects, and more.

Vertigo has a built-in slideshow with 3 different transitions — a horizontal slider, vertical slider, and fade option. No need to purchase any further plugins. 

Vertigo makes customization easy with dozens of options to provide full control over the look and feel of your website, including several color options and professional font choices. The striking layout is retina ready, has 46 built-in social icons & FontAwesome 4.2.

… and the video stacks keep on coming.

Play from Doobox, allows RapidWeaver to place a video background directly behind a stacks page, using either a YouTube video or a self hosted video.

YouTube Videos
Adding a YouTube video as the background is easy, by simply entering the video id, obtained from the videos url at the YouTube website.

Self Hosted Video
Self hosted videos may reside either in your Rapidweaver resources area, or already be present on your server. The stack provides easy settings to link to your video files.

Fully Responsive
Play will remain fully responsive regardless of your video size.

When Realmac Software set out to include some beautifully crafted new themes in RapidWeaver v6, they approached Elixir to be one of the few who would have the honor of having their work included.
The Tesla theme that ships with RapidWeaver 6 comes with a lot of bells and whistles.

Tesla Pro from Elixir Graphics takes things to the next level. It includes a lot of exclusive features that aren't included with the standard version.

Some of its most notable exclusive features are:

• The ability to use your own images as banners
• Several extra stock banners
• 2 ExtraContent areas
• A responsive lightbox for your photo album images
• Our ever-popular Blog Entry topper
• Social media badges
• Additional color pickers
• Font choices for site title, slogan and body type

Tesla is a big, bold theme that let’s your content shine, and gives you flexibility over the way your pages are built. This Pro version will give you even more ways to customize your pages when designing your small business sites, portfolios, blogs and so much more.

Be sure to check out the Tesla Pro product page to read up on all it offers, as well as to check out Elixir's overview and tutorial videos, along with their live preview site.

Will Woodgate has been active again and has released two new stacks.

JumpStack
This useful little stack element can perform two different tasks in your website. Firstly it provides a method to quickly setup manual 'previous' and 'next' navigation links in your webpages, for benefit of both website visitors and search engines indexing your website. These navigation links allow you to connect pages in a sequential order. The other function of this stack element is to generate a TOC (table of contents) which can be used to break-up a large block of content into smaller, linkable regions users can navigate more easily.

uTubeFill
uTubeFill is a free stack element for RapidWeaver, that lets you embed a full-sized, responsive YouTube video on a webpage. This video will be stretched to fill the entire page background. uTubeFill is basically a repackaged version of the popular jQuery Tubular plugin. uTubeFill works well with most ThemeFlood RapidWeaver themes, including Breeze, Photogenic and Splash. Several options are provided to adjust the behaviour of the embedded video. Used in moderation, background video can be used to create very distinctive webpages. Storing the video on YouTube keeps things loading fast and reduces bandwidth.