There is a new kid on the block of (explorer-like) JCR tools: Craig Ching is currently developing a web browser-based application to visualize and edit contents of a Java Content Repository. The application is built upon the Dojo Toolkit and Apache Sling. It will probably make it into the standard Sling releases at some point (see the discussion on the mailing list).
Sling JCR Explorer is not quite ready for production use, but you can find a demo version here (today the site seems to be down, unfortunately). The nice use of Dojo's AJAX capabilities makes it indeed a worth a look.
I welcome this latest addition to the JCR tools arsenal as I do strongly believe that a good set of developer tools is essential for further adoption of JCR. In this context I have compiled a list of JCR tools for browsing repositories that I am aware of. I refrained from doing proper reviews since I am not really impartial. Please find the list below and leave a comment In case I missed a tool.
Hendrik Beck has developed a similar and feature-rich web-based application named JCR-Explorer. One particular useful feature is the ability to observe ongoing changes in the repository (leveraging JCR's observation features).
Day has provided an Eclipse plugin to connect to and manipulate Jackrabbit or CRX-based Content Repositories. The plugin can easily be installed through Eclipse's Update Manager. See the plugin's home page for instructions.
Nodes can be edited and changes be commited one by one. A full list of features is available in Eclipse's Help section once the plugion is installed (for the Catch-22 fans: there is also a section on how to install).
Sandro Böhme has also written an Eclipse Plugin for viewing (but not editing) JCRs and open-sourced it under the Apache License.
In the project's own words:
Visualizes the content of a JSR 170 compliant Java content repository in Eclipse. It focuses on reliability by keeping the scope on displaying the content.
A second Eclipse Plugin focused on simply displaying nodes is Shailesh Mangal's appropriately named JCR Viewer. It seems to have been a by-product of developing the test management tool Zephyr which is based on JCR.
The binaries are available from his blog.