SIL - SOLVER is described as 'SIL Solver® integrates an extensive device database with simplified fault tree analysis equations to provide you with an SIL Verification tool that delivers significant cost and time savings'. There are three alternatives to SIL - SOLVER for Windows and Online / Web-based. The best alternative is Silverly, which is free. Other great apps like SIL - SOLVER are exSILentia (Paid) and SafeGuard Profiler (Paid).
Silverly is helps process safety engineers analyze inherent process risk, set performance targets for safety instrumented functions, and verify that targets are being met according to the ISA 84 / IEC 61511 standard.