Slingshot SEO is a reputable SEO company from Indiana in the US. Why do I say reputable? It has been recommended so often to me along with the one of the founders who specializes in SEO: Jeremy Dearringer. They also have caught my eye during my research of well designed SEO websites more than once.
Lately the Slingshot SEO team has conducted invaluable research that will benefit the whole SEO industry.
It was dealing with conversion attribution. They found out that organic search is widely undervalued.
Besides that I have been following them on various social media and reading the company blog from time to time. I was always impressed with the quality and depth of their contribution to the SEO community and beyond.