Microfi Nitrogen is a native Windows Mobile application that allows you to play songs in several formats (MP3/OGG/AAC/MP4/M4A/3GP/WAV/WMA) on your Windows Mobile Pocket PC device. Nitrogen uses open-source decoders, and is a lightweight, yet powerful application.
Nitrogen features a file browser, custom playlists, full skin support, 10-band equalizer with presets, Shuffle and Repeat modes, a built-in sleep mode, and a command to blank screen to prevent battery drain while playing music.
Nitrogen is lightweight app, built in native C++ code. The open-source application is also available in many languages.
The distinctive feature of Nitrogen is the intuitive finger-friendly interface and kinetic scrolling. It features large buttons and you can browse among your playlist by drawing circles on the screen (tapping in the appropriate space). You can download Nitrogen from the project page.
An active community over at xda-developers has created and made available several skins for Nitrogen.