Absolute Messages module displays system messages in colored horizontal bars on top of the page, similar to Stack Overflow / Stack Exchange network notifications.
Domain Menu Access is an extension to Domain module, allowing administrators to configure visitors' access to selected menu items based on current domain they are viewing.
Administrative overlay is a slick addition to Drupal 7, with all its shiny looks and Ajaxy bells and whistles.
One of the new things introduced in Drupal 7 as compared to D6 is utilization of modified Seven as default administration theme, which - combined with new Overlay module added to core - brings completely new experience to admin pages.
The Drupal Form API provides sophisticated form techniques and also allows for almost unlimited possibilities for custom theming, validation, and execution of forms.
A friend asked me recently how to create a table in Drupal in a proper way.
Let's start with the very basic version - simple header and few rows, only data without any extra attributes.
Here is an example of a basic multistep Drupal form with 3 steps, "Previous" and "Next" buttons on each step and possibility of moving both forwards and backwards in the flow with submitted data being passed on between all steps.
Once a new content field is created, there is no way to change its machine name from administration area. No worries though, this still could be done quite easily by only few updates directly to the database.