Here're just some projects that use Mockito in late 2010. Some entries were contributed by users; some come from analysis of Mockito dependencies in the maven central repository. The list might be out of date but it can give you a feel about the user base. We don't intend to keep the list 100% accurate every day. Feel free to comment.

• Sonar - https://www.sonarsource.org/ - a platform to manage code quality
• Ehcache - https://ehcache.org/ - Java cache
• Dozer - https://dozer.sourceforge.net/ - a Java Bean to Java Bean mapper
• Apache Wicket - https://wicket.apache.org/ - a web framework
• Spring Integration - https://www.springsource.org/spring-integration - Enterprise Integration Patterns implementation for Spring
• Apache Felix - https://felix.apache.org/ - an Apache OSGi implementation
• Hazelcast - https://www.hazelcast.com/ - a clustering and highly scalable data distribution platform for Java
• JWebUnit - https://jwebunit.sourceforge.net/ - Java-based testing framework for web applications
• Hades - https://redmine.synyx.org/projects/hades - a utility library to work with Data Access Objects implemented with Spring and JPA
• FCKeditor Java Integration Core - https://java.fckeditor.net/
• ** JBehave* - https://jbehave.org/ - a framework for Behaviour-Driven Development
• JBoss DNA https://www.jboss.org/dna

Some more projects:

• HBase - https://hbase.apache.org/ - An open-source, distributed, versioned, column-oriented store modeled after Google' Bigtable
• Axon Framework - https://code.google.com/p/axonframework/ - A powerfull framwork that helps to build scalable, extensible and maintainable system using the Command Query Responsibility Segregation (CQRS) architectural pattern
• QuickFIX/J 1.3.3 - https://quickfixj.sourceforge.net
• kouinject - https://code.google.com/p/kouinject/ - Simple dependency injection framework for Java
• t7mp - https://code.google.com/p/t7mp/ - A Tomcat 7 Maven Plugin
• Seam-Perf4j - https://seam-perf4j.sourceforge.net/ - Perf4j integration for Seam Framework
• Many Hudson plugins - https://hudson-ci.org/ - codescanner, gerrit, analysis-pom, serenity, analysis-test, jira, instant-messaging, ...
• Maven plugins - https://maven.apache.org/ - maven-release-manager, clojure-maven-plugin,
• OpenRegistry - https://wiki.jasig.org/display/OR/Home - an OpenSource Identity Management System
• SibillaTest - https://github.com/maeste/SibillaTest/wiki - library for tests
• Convergence - https://www.openspaces.org/display/CVG
• Drizzle JDBC - https://launchpad.net/drizzle-jdbc/ - JDBC Driver for Drizzle
• lambdaj - https://code.google.com/p/lambdaj/ - manipulate collections in a pseudo-functional and statically typed way
• Chameleon - https://wiki.chameleon.ow2.org/ - a simple way to lay out specific OSGi runtimes fitting your requirements
• JGuard - https://jguard.net/ - a library that provides EASY security (authentication and authorization) for Java web applications
• VRaptor3 - https://vraptor.caelum.com.br - Java web MVC framework for fast and maintainable development
• AppInfo - https://appinfo.sourceforge.net/ - Display always current version of your software even when automatically deploying from CI server on QA
• FEST - https://code.google.com/p/fest/ - Fixtures for Easy Software

Scala projects:

• Akka project - https://akkasource.org/ - An actor based concurrency event-driven library
• specsy - https://github.com/orfjackal/specsy - BDD-style unit testing framework for Scala
• specs - https://code.google.com/p/specs/ - a BDD library for Scala
• Lift - https://liftweb.net/ - web framework for Scala

Companies/Commercial products:

• Atlassian use it for Confluence and maybe other products : https://blogs.atlassian.com/developer/2009/01/how_to_make_writing_unit_tests.html
• Adaptivist who create Confluence plugins : https://www.adaptavist.com/display/~jmcgivern/2010/05/09/Unit+Testing+JIRA+with+PowerMock+for+Mockito
• Grid Dynamics a grid computing company : https://blog.griddynamics.com/2010/03/mocking-with-mockito-and-powermock.html
• Altkom Software and Consulting - https://asc.altkom.pl/ - "We were under the impression of features offered by Mockito and the ability to write test code in a clear, short and readable way. After the evaluation in some real projects with a large number of tests Mockito proved its usefulness and was widely adopted by our TDD i Clean Code oriented teams. It was chosen as a base mocking framework for our applications develop in Java."

And many, many others...