MonaCoin (MONA) is the first alternative cryptocurrency developed in Japan, launched in December 2013. It operates as a decentralised and fully distributed payment system, maintained by its community through client applications. MonaCoin is based on the ASCII art character "Mona" and is built on the Lyra2RE(v2) algorithm. It has a block time of 1.5 minutes, a block reward of 12.5 MONA, and a maximum supply of 105,120,000 coins. The block reward halves approximately every three years (every 1,051,000 blocks), and difficulty adjusts with each block using the Dark Gravity Wave v3 algorithm. Importantly, MonaCoin was not premined, meaning all participants had equal opportunity to mine coins from its inception.

MonaCoin is primarily used as a digital currency within its community for various online and offline transactions. The coin gained popularity through grassroots community initiatives rather than centralised development efforts. Users have created MonaCoin-based web applications and services, and it is commonly used for tipping others in online communities, a practice known as "monage" (モナゲ, meaning "throwing mona"). Additionally, the MonaCoin community has integrated the coin into local commerce, particularly in Japan, where some businesses accept MONA for payments. Its decentralised nature makes it suitable for peer-to-peer transactions without reliance on any central authority.

MonaCoin was created by an anonymous developer known as "Mr. Watanabe." The Monacoinproject team developed the main client but does not issue or manage the currency and has no association with any former or current members of Japan's 2channel (now 5channel) internet forum management or its related companies. The development and expansion of MonaCoin have been driven by its user community rather than a centralised development team.