Open Bug Bounty is described as 'non-profit project designed to connect security researchers and website owners in a transparent, respectful and mutually valuable manner. The purpose is to make the World Wide Web a safer place for everyone’s benefit'. There are five alternatives to Open Bug Bounty, not only websites but also apps for SaaS. The best alternative is HackerOne. It's not free, so if you're looking for a free alternative, you could try Bugheist or YesWeHack. Other great sites and apps similar to Open Bug Bounty are SafeHats Bug Bounty (Paid) and Bugcrowd (Free).
Bugheist allows anyone to submit an issue from any website. For example if you saw a broken button on Amazon.com you can report the issue on Bugheist and then get a point! The more bugs you find the more points you get.
Managed bug bounty and vulnerability disclosure programs provide companies with the ability to level the playing field, strengthening the security of products as well as cultivating a mutually rewarding relationship with the security researcher community.