There's a bunch of crypto-currencies out there, with new ones coming up every day. However nearly all of them are based on blockchains, which are distributed ledger-based accounting systems, not really digital cash systems.
HashCash is real digital cash. Like paper cash, it can be transferred directly from person to person and used to make payments instantly and in complete privacy. Unlike paper cash, it can also be sent over the Internet, or just about any communications medium.
The privacy afforded by cash is important in many contexts. It is often critical to protect basic individual rights such as freedom of expression and association. While Bitcoin provides a decentralized medium of exchange, all Bitcoin transactions are published on the blockchain. This makes Bitcoin a poor substitute for cash as it compromises privacy. Bitcoin transaction confirmation is also slow, and transaction fees are on the rise.
HashCash, in contrast, is a close electronic analog of physical cash, and has many of the same properties - it is efficient, flexible, low-cost, and private. What's more, it's quite easy to understand exactly how it works.
HashCash coins are anonymous bearer tokens that provide a level of transaction privacy comparable to paper cash
Verifying HashCash coins takes a few seconds and requires only a tiny amount of data transfer
Low fees (and free-market fee competition between independent vaults). Zero-fee transactions possible
Easy to buy, sell or pay with HashCash using the simple and straightforward cross-platform, multi-lingual wallet
A simple digital cash protocol, implemented in easy-to-understand Perl code, available as free software
HashCash operations are efficient and scalable and don't require large amounts of resources
No possibility of payment reversal, eliminating the uncertainty of chargebacks and fraudulent orders
Enables a decentralized private cash ecosystem based on a free market of competing vaults
HashCash can be used from anywhere and by anyone regardless of access to traditional financial institutions
HashCash is available now as an experimental project for open beta testing