Sound Forge 12.5? I assume your mean Audio Studio 12 (AS-12). SF Pro 12 has not been released yet, but is in the beta test phase.
As your probably aware, Wave Hammer is only available with the purchase of SF Pro, however once installed, it is available on other apps that support DX plugs.
That said, WH is a two-stage dynamics processor.. compressor/limiter and Volume Maximizer. There are many free compressors & maximizers available that would basically do the same thing chained together, however WH has a 'unique' sound. WM's unique' sound aside, I like the Toyko Dawn No. 6 limiter which has five selectable stages, Comp, Peak Limiter, HF Limiter, Clipper and ISP Protect. The updated TDR Limiter 6 GE is available as well but not for free. Other Toyko Dawn plug-ins are certainly worth a look as well.