Developer: Optingun
Price: Optingun offers free plan. Premium plans start from $9. More details can be found here.
Integration Support: Get in contact with Optingun
Optingun helps Online businesses to create amazing forms to convert website visitors into subscribers using action driven popups and Social Optins.
How it works
1. Create or login to your Optingun account and click "Connect your Apps" button.
2. Select “MailerLite” from the list and enter your MailerLite API Key.
3. Create a new form, by choosing MailerLite as your autoresponder integration, and its group, that you want your subscribers to be added.
That's it, you're connected! Now all of your new subscribers will be automatically added to your selected group in your MailerLite account.