Hi @mark-kiernan,
As Jesper says, it depends on the platforms and domains.
– for testing web applications: Selenium (it supports code written in various languages like Java, C#, Ruby etc.)
– for testing desktop applications: HP UFT (formerly QTP) or Ranorex. Both are paid tools and you need a license to use them.
– for API testing: Smartbear (SoapUI, TestComplete etc.) or JMeter.
– for Continuous Integration: Hudson or Jenkins.
Additionally, there are tools like JIRA and TFS (Team Foundation Server) for other testing related activities including bug tracking and project management.
Regards,
Alin