Tryton is a three-tiers high-level general purpose application platform under the license GPL-3 written in Python and using PostgreSQL (or sqlite) as database engine.
To install tryton, build the trytond package from AUR. It may be easier to install this package using yaourt or another package manager that will automatically build this package's dependencies from AUR.
Once Tryton has built, build and install the tryton client, tryton.
As root or using sudo, edit the file /etc/trytond.conf
Here you will find options which you can uncomment and fill out as necessary.
Next, as root, create the directory /var/lib/trytond, and chown it so that the trytond user can access it.
Now you can launch trytond and the tryton client.
Run /etc/rc.d/trytond start as root, and then launch tryton as a regular user.