Written in: C++
Main point: Retains some friendly properties of SQL. 保留类似SQL风格.(Query, index)
License: AGPL (Drivers: Apache)
Protocol: Custom, binary (BSON)
Master/slave replication 主从复制(分布式状态集群方式)
Queries are javascript expressions 查询是javascript表达式
Run arbitrary javascript functions server-side
Better update-in-place than CouchDB 比CouchDB更好地就地更新
Sharding built-in 内置分片碎片
Uses memory mapped files for data storage 使用内存对应文件方式实现数据存储
Performance over features
After crash, it needs to repair tables 当崩溃后，需要修复表。

适用: 需要动态查询. 愿意事先定义索引indexes, 不需要 map/reduce 功能. 你需要巨大的数据库有良好性能，你需要CouchDB但是你数据变化改变很频繁，需要频繁写。

举例: 适合所有MySQL 或者 PostgreSQL场合，它也适合

Cassandra

Written in: Java
Main point: 大表模型BigTable 和 Dynamo中最好的
License: Apache
Protocol: Custom, binary (Thrift)
Tunable trade-offs for distribution and replication (N, R, W)
Querying by column, range of keys 按列查询
BigTable-like features: columns, column families 列
Writes are much faster than reads (!) 写快于读
Map/reduce possible with Apache Hadoop
部分复杂性可能由于Java自身原因(如配置configuration, seeing exceptions, etc)

适用: 当写操作多于读操作 (如日志logging).

举例: 银行Banking, 金融系统，写必须快于都的场合，实时的数据分析等.

Riak

Written in: Erlang & C, some Javascript
Main point: 容错性Fault tolerance 失败恢复可靠性好
License: Apache
Protocol: HTTP/REST
Tunable trade-offs for distribution and replication (N, R, W)
Pre- and post-commit hooks,
for validation and security.
Built-in full-text search 内置全文本搜索
在 Javascript 中Map/reduce 或 Erlang 支持
Comes in "open source" and "enterprise" editions 有两个版本

适用: 如果你希望有类似Cassandra-like (Dynamo-like)风格, 但是你不想处理器复杂性和膨胀性。单服务器有良好可伸缩性scalability, 可用性availability 和容错性 fault-tolerance, 采取是昂贵的多站点复制multi-site replication.

举例: 销售点数据收集，工厂控制系统，那些不能允许几秒当机的场合。

HBase

(With the help of ghshephard)

Written in: Java
Main point: 十亿级别的行 X 百万级别的列大容量
License: Apache
Protocol: HTTP/REST (also Thrift)
Modeled after BigTable 大表模型
Map/reduce with Hadoop 内置Map/reduce
Query predicate push down via server side scan and get filters
Optimizations for real time queries 能够实时获得基于查询的优化
A high performance Thrift gateway 高性能的Thrift型网关
HTTP supports XML, Protobuf, and binary
Cascading, hive, and pig source and sink modules
Jruby-based (JIRB) shell
No single point of failure 无单点风险
Rolling restart for configuration changes and minor upgrades
Random access performance is like MySQL 随机访问的性能类似MySQL

适用: 如果你喜欢大表模型BigTable. :) 你需要随机实时的读写操作

举例: Facebook 消息数据库

当然，所有这些数据库系统都有比列在这里多得多的功能特性。我这里仅仅依据我个人认识列出一些关键特性，并且这些项目的开发也很活跃，我将尽力保持更新。

-- Kristof

来源：http://kkovacs.eu/cassandra-vs-mongodb-vs-couchdb-vs-redis