Slant is described as 'product recommendation community that helps connect people with the best products for them. You shouldn’t have to waste time and money to find solutions to your problems' and is a well-known website in the Online Services category. There are more than 50 alternatives to Slant, not only websites but also apps for a variety of platforms, including Android, iPhone, Mac and Windows. The best alternative is AlternativeTo, which is free. Other great sites and apps similar to Slant are Reddit (Freemium), Product Hunt (Free), Quora (Free) and SimilarSites (Free).
When I am exploring alternatives to a product or service, I often to go Google, type "[product] vs ", and just see what it autocompletes. That usually tells me the most popular competitors. If I want to be thorough I'll do the same for the competitors, etc.
WikiSpooks is a global alternative encyclopedia on politics, spy craft, deep state intelligence, and conspiracies, free of corporate influence, partisan politics, or government propaganda for historians and truth-seekers to read, edit, and share.
Similarto has close to 2 million websites in its database. The site competes with sites like siteslike.com, similarsites.com, and moreofit.com. What that means is that you could find alternative site for almost any site.