"Falsework consists of temporary structures used in construction to support spanning or arched structures in order to hold the component in place until its construction is sufficiently advanced to support itself." —Wikipedia
In the Drupal website development, a lot of modules get used during the development process but are either disabled or fade into the background.
Devel and Theme developer
CVS Deploy, Git Deploy, Update Settings Advanced, etc.
Database logging / Syslog (both in core)
various API modules