re:AMP - Audio player for Mac with Winamp classic skins support
K-Lite Codec Pack - K-Lite Codec Pack is a collection of codecs, DirectShow filters and tools.
Audioread (formerly Audiblogs) - Audiblogs lets you listen to any web article in your podcast player in an Audible-like voice.
AC3Filter - AC3Filter is a high quality free audio decoder and processor filter.
Overcast - Video-first asset management for teams
CCCP: Combined Community Codec Pack - The CCCP: Combined Community Codec Pack is a codec pack specifically built for playing videos (including mkv).