One of the questions that is often asked of open source software is, "Who's using it?" The idea is that if others are using the software, it must be okay and safe for use. Although Quartz has been around for quite a while, it's just recently starting to get the attention it deserves from the development community.
The list of users and projects that are using Quartz is quite impressive.You can find the list on the Quartz Wiki at http://wiki.opensymphony.com/display/QRTZ1/Quartz+Users. Probably what's most impressive is the number of other well-known open source projects that include Quartz as part of their software: Among them are JIRA, Spring, and several Jakarta projects.
There's no real way to gauge how many users are actively using Quartz in "real" projects. But judging from the download numbers and some of the high-profile projects that are currently using Quartz, it looks like the number of users is many thousandsand on the rise.
Scheduling in the Enterprise
Getting Started with Quartz
Hello, Quartz
Scheduling Jobs
Cron Triggers and More
JobStores and Persistence
Implementing Quartz Listeners
Using Quartz Plug-Ins
Using Quartz Remotely
Using Quartz with J2EE
Clustering Quartz
Quartz Cookbook
Quartz and Web Applications
Using Quartz with Workflow
Appendix A. Quartz Configuration Reference