Here's how to use the field group module and form API in Drupal 7 to create a form with horizontal tabs.

"Fieldgroup will, as the name implies, group fields together. All fieldable entities will have the possibility to add groups to wrap their fields together. Fieldgroup comes with default HTML wrappers like vertical tabs, horizontal tabs, accordions, fieldsets or div wrappers."

"CER keeps reference fields in sync. If you have two entities that refer to each other using Entity Reference (or some other kind of reference field), it saves you the trouble of double-editing your entities in order to have them point at each other. If entity Alice references entity Bob, CER will make Bob reference Alice, and keep the references up-to-date when either entity is updated or deleted."

Maintained by Dave Reid, Earl Miles, Damien McKenna and Derek Wright

This module give each user the ability to choose which language the admin interface is in.

This module automatically saves form states using jQuery Sisyphus

Smart Trim implements a new field formatter for textfields (text, text_long, and text_with_summary, if you want to get technical) that improves upon the "Summary or Trimmed" formatter built into Drupal 7

With the Field Conditional State module you can change the state of any supported fields form element depending on the content of other fields. This is done by providing an UI for Drupal's States API. All the changes made to a form by FCS (Field Conditional States) utilize only the States API and therefore are clientside only.

This module is basically the Drupal 7 successor to CCK 3's Multigroup in Drupal 6. A similar module is the Inline Entity Form. Caution: ...

This module "allows permissions to be set to each field within the Authoring information and Publishing options field sets on the node form. It also allows selected field sets to be set as collapsed and / or collapsible."