I think that the best online marketing tools are still marketing materials that can be shared to social media or attached in the right email template.
For this, I would recommend a tool like Tweak Cloud (
https://www.tweak.com/) because it will help you to maintain your brand integrity whilst you can design, edit and create all new designs from over a million professionally-designed templates for brochures, flyers, leaflets, postcards, business cards etc.
Editing takes place in conjunction with Adobe InDesign and is really useful because it's got a share button and can be uploaded to your socials straight away.