symfony/skeleton and symfony/website-skeleton

Came here as a result of a similar search, but was more interested in what's under the hood.

Not to take away from the accepted answer, but for those who, like me, were after something more detailed, you can look at the package details in packagist and reviewing the dependencies noted in the requires and requires dev sub-sections:

https://packagist.org/packages/symfony/website-skeleton

Includes: framework, framework extra, console, asset, security, validator twig, doctrine, http client, serialiser, yaml, dotenv, flex, form and validator packages among others.

https://packagist.org/packages/symfony/skeleton

Includes: console, dotenv, flex, platform and yaml only.

Seems like a no brainer, but if you came here looking for it, it's there.

The new symfony edition (Symfony 4) is "bundle less". Symfony core team decided to not provide the Symfony Standard Edition for Symfony 4.0 that means when you run composer create-project symfony/skeleton you download the minimum package to start an application and you have to download the over packages needed and you need to explicitly add all the dependencies you want to depend on (twig, routing...) look here for other package . But it could be difficult for new comers and the Symfony core team dediced to provide an edition with the minimum common Symfony features. You get it with composer create-project symfony/website-skeleton. You have more explanation here