Maven Repository managers serve two purposes: they act as highly configurable proxies between your organization and the public Maven repositories and they also provide an organization with a deployment destination for your own generated artifacts.
Proxying a Maven repository brings a number of benefits. Proxying speeds up builds throughout your organization by installing a local cache for all artifacts from the Central Maven repository. If a developer in your organization needs to download version 2.5 of the Spring Framework and you are using a Maven Repository Manager, the dependencies (and the dependency's dependencies) only need to be downloaded from the remote repository once. With a high-speed connection to the Internet this might seem like a minor concern, but if you are constantly asking your developers to download hundreds of megabytes of third-party dependencies, the real cost savings are going to be the time it takes Maven to check for new versions of dependencies and to download dependencies. Serving Maven dependencies from a local repository can save you hundreds of requests over HTTP, and, in very large multi-project builds, this can shave minutes from a build.
If your project is relying on a number of SNAPSHOT dependencies, Maven will need to check for updated version of these snapshots. Depending on the configuration of your remote repositories, Maven will check for SNAPSHOT updates periodically, or it might be checking for SNAPSHOT updates on every build. When Maven checks for a snapshot update it needs to interrogate the remote repository for the latest version of the SNAPSHOT dependency. Depending on your connection to the public Internet and the load on the central Maven repository, a SNAPSHOT update can add seconds to your project's build for each SNAPSHOT update. When you host a local repository proxy with a repository manager, your repository manager is going to check for SNAPSHOT updates on a regular schedule, and your applications will be able to interact with a local repository. If you develop software with a lot of SNAPSHOT dependencies, using a local repository manager can often shave minutes from a large multi-module project build, your 5-10 second SNAPSHOT update checks against the public central repository are going to execute in hundreds of milliseconds (or less).
In addition to the simple savings in time and bandwidth, a repository manager provides an organization with control over what is downloaded by Maven. You can include or exclude specific artifacts from the public repository, and having this level of control over what is downloaded from the central Maven repository is a prerequisite for organizations which need strict control over what dependencies are used throughout an organization. An organization which wants to standardize on a specific version of a dependency like Hibernate or Spring can enforce this standardization by only providing access to a specific version of an artifact in a repository manager. Other organizations might be concerned with making sure that every external dependency has a license compatible with the legal standards of that organization. If a corporation is producing a application which is distributed, they might want to make sure that no one inadvertently adds a dependency on a third-party library which is covered under a copy-left license like the GPL. Repository managers provide for the level of control that an organization needs to make sure that overall architecture and policy can be enforced.
Aside from the benefits of mediating access to remote repositories, a repository manager also provides something essential to full adoption of Maven. Unless you expect every member of your organization to download and build every single internal project, you will want to provide a mechanism for developers and departments to share both SNAPSHOT and releases for internal project artifacts. A Maven repository manager provides your organization with such a deployment target. Once you install a Maven repository manager, you can start using Maven to deploy snapshots and releases to a custom repository managed by the repository manager. Over time, this central deployment point for internal projects becomes the fabric for collaboration between different development teams.
The Following is a list of the known Maven repository managers and listed in alphabetical order:
Apache Archiva is an extensible repository management software that helps taking care of your own personal or enterprise-wide build artifact repository. It is the perfect companion for build tools such as Maven, Continuum, and ANT.
Archiva offers several capabilities, amongst which remote repository proxying, security access management, build artifact storage, delivery, browsing, indexing and usage reporting, extensible scanning functionality... and many more!
Artifactory is a Maven 2 enterprise repository. It offers advanced proxying, caching and security facilities to provide a robust, reproducible and independent build environment when using Maven. Artifactory is being used by clients ranging from small startup teams to international corporate teams employing distributed development, thus improving the development experience for tens of thousands of developers. Artifactory exposes a robust artifacts management platform using rich Ajax web UI and can be run out-of-the-box with a simple "unzip and launch".
Anyone who was using Proximity is now encouraged to use Nexus. The entire codebase of Proximity was absorbed into Nexus and Nexus provides a migration path for all Proximity users.
Tamas Cservenak started working on Proximity in December 2005 as he was trying to find a way to isolate his own systems from an incredibly slow ADSL connection provided by a Hungarian ISP. Proximity started as a simple web application to proxy artifacts for a small organization with connectivity issues. Creating a local on-demand cache for Maven artifacts from the central Maven repository gave an organization access to the artifacts on the Central Maven Repository, but it also made sure that these artifacts weren't downloaded over a very slow ADSL connection used by a number of developers. In 2007, Sonatype asked Tamas to help create a similar product named Nexus. Nexus is currently considered the logical next step to Proximity. Nexus currently has an active development team, and portions of the indexing code from Nexus are also being used in m2eclipse