CertExams.com has recently released a network simulator for JUNOS(TM) software, with support for a limited command set. The details can be viewed at Juniper(R) JUNOS Simulator page. This is the most recent stable release of the software from CertExams.com. Earlier network simulators include
CCNA Network Simulator with Online Tests
CCNA Network Simulator with Designer, and
CCNA Router Simulator
On-line tests for several vendor IT certifications are also available at online.certexams.com
The available on-line tests include:
A+ Core practice tests
A+ OS practice tests
CCNA practice tests
PHP practice tests, and others.
More information is available at certexams.com