DITA may have begun with IBM, but it is now controlled by Oasis. PTC/Arbortext was the only vendor invited to be a charter member of the Oasis DITA Technical Committee. IBM was using Arbortext when they developed DITA, in fact.
PTC has a fully-functional, enterprise-level DITA solution: Arbortext Editor, Publishing Engine, and Content Management System. DITA is fully supported. Specializations require no additional programming (beyond the DTD/schema creation) to implement in Arbortext.
This week's podcast features Robin Sloan from PTC.
Robin Sloan is a name everyone in the Arbortext community knows. Robin is a Product Manager in the Arbortext business unit. She was part of Arbortext prior to the acquisition. Robin was integral in designing the modularity of the DITA stylesheets that ship with Arbortext Editor, Styler, and Publishing Engine. PTC still maintains a DITA answers mailing list that Robin answers.
It's my pleasure to interview Robin about getting started with Arbortext and DITA. There's knowledge she has that nearly no one else knows and she's eager to share.