Stand-alone application StitchBuddy
Its main purpose is to preview changes of a design’s thread colors, but I added some more features: Designs can be flipped and rotated by 45° and it’s possible to center a design in its hoop. Based on the StitchBuddy framework the application can read JEF, PES, SEW, EXP, and DST embroidery files. Unfortunately I didn’t find enough information to write PES, so saving designs is limited to JEF, EXP, and DST.
StitchBuddy can be purchased for USD 25 / EUR 20.