What
Group of test tools produced by IBM Rational. Closely aligned with the Rational Unified Process (RUP). Although they can be used independently. An overview of testing in the RUP is available.

I would include in this group :--Rational Robot, Rational Team Test, Purify as pure test tools.

Other Rational tools which the tester may come across are RequisitePro and ClearCase. These are more closely aligned with requirements and analysis.

Who?
Rational was an independent company until it was brought by IBM. The nearest competitor is Mercuryinteractive.

Where?
Geographically everywhere IBM is.

In develepment terms, all through the lifecycle.

When?
Inception, Elaboration, Construction and transition. Also along both slopes of the V Model.