SpectreRF is an option to the Spectre Circuit Simulator from Cadence Design Systems.
It adds a series of analyses that are particularly useful for RF circuits to the basic capabilities of Spectre.
First, it was arguably the first RF simulator in that it was the first to be designed for large bipolar and CMOS RF circuits; it used shooting methods as its base algorithm; and it pioneered the use of Krylov subspace methods.
Eventually the dominance of SpectreRF faded as the use of Krylov subspace methods propagated to other simulators, particularly those based on harmonic balance.
SpectreRF was developed by Ken Kundert, Jacob White, and Ricardo Telichevesky.