WinMX is a peer-to-peer file sharing program authored by Frontcode Technologies. WinMX began its life as an OpenNap client capable of connecting to several servers simultaneously, although Frontcode later , starting with WinMX 2, created a proprietary protocol, termed WinMX Peer Network Protocol (WPNP). WPNP version 2 was phased out as WinMX 3.0 and its WPNP version 3 protocol came into existence. Frontcode operates several cache servers to aid WPNP network operation.
Lopster used to have WPNP 2 support, although it was locked out with the arrival of WPNP 3.
WinMX was very popular in Japan due to its ability to handle 2 byte characters. By 2001 it was the defacto P2P application in Japan. However, WinMX's Japanese popularity dropped sharply with the arrest of several users, and resulted in the development of a semi-secure, encrypted, serverless application called WinNY (N comes after M, Y comes after X).