However, it is still possible to get a native copy running on your Ubuntu.
Please refer to this askubuntu post if the below method does not work for you (because it is probably already outdated).
On Ubuntu 12.04:
You'll need to add two repositories, one for Sigil and one for a dependency, then update repos, and install:
sudo add-apt-repository ppa:sunab/sigil-git sudo add-apt-repository ppa:beineri/opt-qt521 sudo apt-get update sudo apt-get install qt52base qt52webkit sudo apt-get install sigil