Synfig Studio is a free and open-source 2D animation software, designed as powerful industrial-strength solution for creating film-quality animation using a vector and bitmap artwork. It eliminates the need to create animation frame-by frame, allowing you to produce 2D animation of a higher quality with fewer people and resources. Synfig Studio is available for Windows, Linux and MacOS X.
Animation created with Synfig Studio can be exported to GIF, MPG, FLV, and more! So, if you're looking for a free application for creating 2D animation, Synfig Studio is a worth trying solution!

Below are Synfig Studio features headline taken from its official website:
  • Spatial resolution-independence
  • Temporal resolution independence
  • High Dynamic-Range Imaging (HDRI)
  • Pentablet-friendly tools
  • Artist-oriented design
  • Path-based Gradients
  • Supports a multitude of layers of various types
For further information about Synfig Studio features, please refer to its website.

Install Synfig Studio on Ubuntu
Synfig Studiois unavailable on Ubuntu repository and there is no PP yet. So, you should download its *.deb installer here. Once downloaded, type the following commands to install it:
  • sudo dpkg -i synfigstudio_0.62.02-20101113.master.1_i386.deb
  • sudo apt-get -f install
For additional information, below is a sample animation created with Synfig Studio:

Regards :)