This is a technical description of the 3.x branch of the module. For the newer 4.x branch, see this article.
Simple XML sitemap 3.0 has been released
The third major version of simple_sitemap has been seven months in the making. The module has been rewritten from the ground up and now features a more reliable generation process, a significantly more versatile API and many new functionalities.
Major new features
Ability to create any type of sitemap via plugins
The 8.x-3.x release allows not only to customize the URL generation through URL generator plugins as 2.x did, but also creating custom sitemap types that mix and match a sitemap generator along with several URL generators to create any type of sitemap.
This 3-plugin system coupled with the new concept of sitemap variants makes it possible to run several types of sitemaps on a single Drupal instance. Now e.g a Google news sitemap can coexist with your hreflang sitemap.
A sitemap variant can but does not need to be coupled to entity types/bundles. When creating a sitemap generator, one can define where the content source is located and what to do with it upon sitemap generation/deletion.
Ability to create sitemap variants of various sitemap types via the UI
In 3.x links form a specific entity bundle can be indexed in a specific sitemap variant with its own URL. This means, that apart from /sitemap.xml, there can be e.g