You can sell tickets from your own web pages with very little coding. These widgets are open source and the full documentation can be found on GitHub.
A calendar component that displays the dates for an event.
"Get your tickets" button
A CSS stylesheet for the purchase link in your web pages.
The Koliseo API is available for commercial and non-commercial use by third-party developers and can be used for all sorts of integrations. The documentation of the API is an ongoing project, and only features that are considered stable are getting public. Anything that is not mentioned here should not be considered final.
The API documentation is available on Mashape.