I believe these 2 are Ubuntu specific and made a big impact:

• Ubuntu Software Center is a utility for installing, removing, and purchasing software in Ubuntu. It replaces several other utilities, which makes the overall experience easier to understand, improves user safety, and frees space on the Ubuntu CD. The next version will be 3.2, allowing ratings and reviews of software. Later versions may include recommendation features, replace Synaptic, APTonCD, and most of the Computer Janitor, and integrate with Update Manager.

From muktware.com: "We already agreed that we would like the current Ubuntu Software Center to be improved and used in various distributions. If this happens, then we will have the same software center in many distributions, but this doesn't mean that the available applications have to be exactly the same in every distribution. There are no plans to merge software repositories for now, nor package managers."

Samuel Verschelde (aka Stormi), Mageia contributor, mageia-app-db project lead.

• Upstart is an event-based replacement for the /sbin/init daemon which handles starting of tasks and services during boot, stopping them during shutdown and supervising them while the system is running. It was originally developed for the Ubuntu distribution, but is intended to be suitable for deployment in all Linux distributions as a replacement for the venerable System-V init.