Justin Frankel is an American computer programmer best known for his work on the Winamp media player application and for inventing the Gnutella peer-to-peer network. Frankel is also the founder of Cockos Incorporated, which creates music production and development software such as the REAPER digital audio workstation, the NINJAM collaborative music tool and the Jesusonic expandable effects processor.

Winamp is a media player for Microsoft Windows originally developed by Justin Frankel and Dmitry Boldyrev by their company Nullsoft, which they later sold to AOL in 1999 for $80 million. It was then acquired by Radionomy in 2014, now known as the Llama Group. Since version 2 it has been sold as freemium and supports extensibility with plug-ins and skins, and features music visualization, playlist and a media library, supported by a large online community.