dotXSI
From Just Solve the File Format Problem
dotXSI (or XSI format) is a scene format associated with the Softimage (formerly Softimage|XSI) 3D graphics software. It is a text-based format, related to DirectX .X format.
There is also a binary version of it: Softimage SCN.
See also Softimage PIC.
Identification
Files most likely begin with "xsi 0
".