Here's how to get ikiwiki. See setup for how to use it, and be sure to add your wiki to IkiwikiUsers if you use ikiwiki.
tarball
The best place to download a tarball of the latest release is from http://packages.debian.org/unstable/source/ikiwiki.
Installation steps and requirements are listed on the install page.
packages
If using Debian (since 4.0), or Ubuntu (since 6.10):
Note that Debian 4.0 and especially Ubuntu 6.10 contain older versions of ikiwiki, there have been lots of enhancements and bug fixes since those versions.
apt-get install ikiwiki
Or download the deb from http://packages.debian.org/unstable/web/ikiwiki.
There is a backport of a recent version of ikiwiki for Debian 4.0 at http://packages.debian.org/etch-backports/ikiwiki.
There is also an unofficial backport of ikiwiki for Ubuntu Gutsy and Ubuntu Hardy, provided by Paweł Tęcza, at http://gpa.net.icm.edu.pl/ubuntu/.
Also, FreeBSD has ikiwiki in its ports collection.
And Gentoo has an ebuild in its bug database.
revision control
Ikiwiki is developed in a git repository.