What newsletter platforms do people use?

For building an audience I know growing an email list is important, but I am curious what tools people use for growing a newsletter.

How are you building your audience to drive traffic to your side project?

I am currently growing emailemu.com, but have been just using an email input form on my wfeaster.com/newsletter then manually grabbing the address and adding them into my Mailchimp

Wondering if there is a better way?