Lifetime license. Once-off payment.
Intro.js is AGPL-licensed and open-source. However, if you want to use Intro.js in your commercial app, website or plugin, you would need to obtain a commercial license.
One project
No commercial support
Regular product updates
Lifetime license
5 projects
1 month commercial support
1 custom theme
Regular product updates
Lifetime license
Unlimited projects
6 months support
3 custom themes
24/7 Priority Support
Lifetime license