Sendwithus has a free account for up to 1,000 recipients. They also offer A/B testing, among other features. But as BellaOnline has its own email system, I was interested in their Open Source Email Templates Project. These templates are responsive for most email clients (readers). What I like the best is that the templates have been tested with Litmus, an email testing tool.
You can download just one template or use the link to download all of them in a zip. Once unzipped, each template has a folder and inside the folder are HTML files for each version. Once you customize the template with your images and text, just paste the HTML into your email system. Check the links at the bottom for more detail about Sendwithus and the Open Source Email Templates Project.
At this time, the Open Source Email Templates Project has 14 email templates. Most have placeholder images and text. But for those who wish to start from scratch, there is the Cerberus template. Let's start there.
Cerberus by Ted Goas
This template comes in three versions, Fluid, Hybrid and Responsive. It's nice that the creator of the template has documentation.
http://tedgoas.github.io/Cerberus/
Plain-jane
This template is a plain HTML text email.
Mantra by Email Monks
This template has nine versions ranging from Welcome to Coupon and Receipt.
Meow by ZURB
This template is built with Foundations for Emails. ZURB offers an email master class, but it's not free.
Zurb Master Class
http://zurb.com/university/responsive-emails-foundation
Foundation for Emails
http://foundation.zurb.com/emails.html
Skyline, Sunday, Oxygen and Neapolitan
For those modern and chic blogs, these templates are for you. You will like the large header image.
Goldstar by MailBakery
A classic style with solid colored background and corner design
Go
A flexible two-column template
Airmail, Cleave, Narrative and Zen-flat
These templates have a very minimal style, with a lot of open white space.
Sendwithus Links
Open Source Email Templates Projecthttps://www.sendwithus.com/resources/templates/about
https://www.sendwithus.com/resources/templates
How to Send Email Like a Startup
https://www.sendwithus.com/resources/guide
Email Layout Generator
https://www.sendwithus.com/resources/generator
Preheader Blog
https://preheader.com/
Litmus
https://litmus.com/
Disclosure: The opinions are completely my own based on my experience.