Export OMF From Nuendo or Cubase to Reaper
Nuendo and Cubase (both from Steinberg) share the same OMF exporter, so the steps are identical whichever one you're using.
Select File > Export > OMF. In the export options, pick which tracks to include and choose an OMF version — if you're not sure which the receiving software expects, the newer version is the safer default.
You can also choose whether to embed the audio in the OMF file itself or keep it as separate referenced files — either is fine for converting.
Reaper doesn't open .omf files on its own, so once you have the export, convert it into a Reaper project.
You can convert your OMF file for free here.
A 2-minute walkthrough of how to open an OMF file in Reaper, from start to finish.
Everything you need to know about OMF files and Reaper: how to open an OMF in Reaper, how OMF exports work (embedded vs. non-embedded), what they contain, what's missing, and what used to break before this converter existed.