Other than Boomerang these are best if you're already using one for marketing purposes or if you're looking to create a customer facing training series that you want to deliver via email. I wouldn't recommend going the email method for internal courses and signing up for a specific service only for that.
If you're building a website it's best to either use your marketing site for something external (don't add on more systems if you can help it!), or for something internal make sure it's something you can password protect. Most CMS systems should let you add a password.