Seasar2 is an open source

Open source

The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 application framework

Application framework

In computer programming, an application framework consists of a software framework used by software developers to implement the standard structure of an application for a specific development environment ....

 similar to the
Spring Framework (Java)

Spring Framework (Java)

The Spring Framework is an open source application framework for the Java platform.The first version was written by Rod Johnson, who released the framework with the publication of his book Expert One-on-One J2EE Design and Development in October 2002. The framework was first released under the...

. Initially, it was developed for the Java platform by Yasuo Higa, but .NET

.NET Framework

The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...

 and PHP

PHP

PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...

 platforms are currently supported as well.
Seasar2 has a large base of Japanese users, but there is a steady increase of
non-Japanese users since English support was announced at the JavaOne

JavaOne

JavaOne is an annual conference inaugurated in 1996 by Sun Microsystems to discuss Java technologies, primarily among Java developers. JavaOne is held in San Francisco, California typically running from Monday to Thursday. Technical sessions on a variety of topics are held during the day. In the...

 2005 Tokyo conference.

Seasar2 is currently supported by the Seasar Foundation, a non-profit open source organization.
Seasar was initially made public on August 2003 at SourceForge

SourceForge

SourceForge Enterprise Edition is a collaborative revision control and software development management system. It provides a front-end to a range of software development lifecycle services and integrates with a number of free software / open source software applications .While originally itself...

.jp as an
application server using Jetty (web server)

Jetty (web server)

Jetty is a pure Java-based HTTP client/server, WebSocket client/server and servlet container developed as a free and open source project as part of the Eclipse Foundation...

 and HSQLDB

HSQLDB

HSQLDB is a relational database management system written in Java. It has a JDBC driver and supports a large subset of SQL-92 and SQL:2008 standards. It offers a fast, small database engine which offers both in-memory and disk-based tables...

.
The name was coined by the initial developer Yasuo Higa after an Okinawan mystical creature Shisa

Shisa

Shisa is a traditional Ryukyuan decoration, often in pairs, resembling a cross between a lion and a dog, from Okinawan mythology. People place pairs of shisa on their rooftops or flanking the gates to their houses. Shisa are wards, believed to protect from some evils...

.

On March 2004, Seasar was re-introduced as light weight dependency injection

Dependency injection

Dependency injection is a design pattern in object-oriented computer programming whose purpose is to improve testability of, and simplify deployment of components in very large software systems....

 and AOP

Aspect-oriented programming

In computing, aspect-oriented programming is a programming paradigm which aims to increase modularity by allowing the separation of cross-cutting concerns...

 container and renamed Seasar2.