Open Music Score aims to provide public domain music scores in the open and editable format of MusicXML. All registered members of OMS may share any public domain score they wish. You can read up more on MusicXML format here: MusicXML.
Files on OMS are almost exclusively MusicXML files. These can be opened by most music engraving applications such as Finale and Sibelius, as well as, the free and open source alternative, MuseScore, which we highly recommend if commercial options are not an option for you. Click here for a full list of MusicXML programs.
If you have public domain scores in a well-edited form, you can use your engraving application to export it to MusicXML. You can then create a new article and attach the file in an XML (.xml/.mxl) format. You can request additional music categories in the forum. For details read Step by Step: How to Contribute.