This is PHP Composer, debianized.
This is packaged on Launchpad, at https://launchpad.net/composer.
Add the PPA:
apt-add-repository -y ppa:duggan/composer
apt-get update
Then install with:
apt-get install php5-composer
Releases are tagged with a date, as the composer project itself does not hold to any useful versioning mechanism.
The PPA is set up for daily builds, though I expect this to settle into a roughly weekly cadence of release.
To update:
apt-get update
apt-get install --only-upgrade php5-composer
Updating this just requires running “update.sh” from the root of the repository (and pushing the result to master, along with the the tags). After that, the imports and source package recipes on Launchpad take care of the builds.