The best replacement for specflow is mspec.

The best alternatives to specflow are rated as following:
★★★★★  mspec
★★★★  nbehave
★★★★  cucumber
★★★★  fitnesse
★★★  storyq

Your alternative for specflow is not listed? Suggest!
Speaking about specflow, one probably shouldn't forget about watin.

Other search terms related to specflow and their ratings are:
★★★★★ watin
You have in mind a companion for specflow and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of specflow in all years. Click on graph for more.
specflow
mspec
nbehave