However, O2Jam was an online service with a monthly fee, limited song rotations, and eventual shutdowns in various regions. O2Mania solved all of these problems:

In simple terms, O2Mania is a for O2Jam (and other games). It allows you to play .ojm (audio) and .ojn (note chart) files directly on your hard drive without needing an internet connection or an active game server.

Disclaimer: O2Mania is an unofficial fan project. You will need to source your own music files legally.

Unzip the contents to a folder like C:\Games\O2Mania\ . Do not use Program Files (Windows permissions can cause save/settings issues).