A month ago we started the Drupal 8 alpha cycle to encourage module developers to test out Drupal 8 and to try upgrading their modules. Today, we published the second alpha release of Drupal 8: Drupal 8.x alpha 2!
I think it is exciting that after years of hard work by many, we have now begun to post alpha releases.
The purpose of alpha releases is to allow module developers to identify API deficiencies while they can still be corrected. We want Drupal's API to be easy to learn, easy to use (even without documentation), hard to misuse, easy to read and maintain, and easy to extend. Good API design really matters and we only have one chance to get it right so please download the alpha release, try upgrading some contributed modules, and provide us feedback along with suggestions for improvement.
Time is of the essence as API changes to Drupal 8 are only allowed for a little longer. We're about to enter the polish phase of the Drupal 8 development cycle, where we will soon switch to beta releases and no longer allow API changes unless needed to fix release blocking issues. From then on, most API improvements will have to wait until Drupal 9.
— Dries Buytaert