1. Email Service Providers (ESPs): Platforms like Mailchimp, Constant Contact, and Sendinblue. 2. Analytics Tools: Google Analytics, Kissmetrics, and other data analysis software. 3. Design Tools: Canva, Adobe Creative Cloud, and other graphic design software. 4. Automation Tools: HubSpot, ActiveCampaign, and other marketing automation platforms. 5. A/B Testing Tools: Optimizely, Unbounce, and other testing platforms.