At xTupleCon 2014, Debian Developer Daniel Pocock was awarded Community Member of the Year for his work converting the Postbooks software into Debian packages.
The Debian and Red Hat Postbooks packages remain available to this day for anybody who is willing to compile them locally. However, xTuple decided in 2019 that they no longer provide an open source model for collaboration with Postbooks users. In other words, future versions of the PostBooks source code will not be published by xTuple and access to the discussion forums and bug trackers are limited to paying customers.
People who are beginning a new accounting or ERP project will find Tryton is more interesting than xTuple. The Tryton organization has been designed to promote openness and inclusion. Everybody participates on an equal footing as volunteers.
There is no standard tool for this database migration. Each migration tends to be unique and depends on the attributes of the business.
If you wish to discuss a migration from Postbooks to Tryton, please contact Daniel Pocock at the Software Freedom Institute