Metapop is described as 'community of music makers of all levels and backgrounds who create, learn and connect together. Sign up for Metapop today to connect with other music makers, give and receive feedback on tracks and collaborate on songs:' and is an website in the Audio & Music category. There are six alternatives to Metapop, not only websites but also apps for a variety of platforms, including Android, iPhone, Android Tablet and iPad. The best alternative is SoundCloud, which is free. Other great sites and apps similar to Metapop are Audius Music (Free, Open Source), hearthis.at (Freemium), Clyp (Paid) and SoundClick (Free).
Audius is a streaming platform built for all musicians, not just those signed to labels. Build a fanbase, share your works in progress, and then publish your completed tracks for all the world to hear.
SoundClick is a music-based social community. It offers bands, artists, and music labels a platform for self-promotion. Songs can be streamed, downloaded in MP3 format, sold through the store, or licensed to others.
A blip is a combination of 1) a song and 2) a short message that accompanies it. The way you create a blip is to first search for a song that you want to hear (or a song that you want your listeners to hear), then add a short message (under 150 characters), finally you submit it.