There are several social sharing platforms available that can be integrated into a PHP website. Some of the popular platforms include:

1. AddThis: AddThis provides social sharing buttons that can be easily added to your PHP website. It supports various social media platforms like Facebook, Twitter, LinkedIn, Pinterest, and more.

2. ShareThis: ShareThis is another popular social sharing platform that allows users to share content to various social media platforms. It provides customizable sharing buttons and analytics to track shares and engagement.

3. Shareaholic: Shareaholic offers various social sharing and content amplification tools for websites. It supports popular social media platforms like Facebook, Twitter, Pinterest, LinkedIn, and more.

4. Share Buttons by AddToAny: AddToAny provides customizable sharing buttons that can be integrated into your PHP website. It supports over 100 social media platforms, including Facebook, Twitter, LinkedIn, Pinterest, and more.

5. Social Share Kit: Social Share Kit is an open-source social sharing library that provides customizable sharing buttons for Facebook, Twitter, Google Plus, LinkedIn, and more. It can be easily integrated into a PHP website.

These platforms offer easy integration options and provide customizable sharing buttons that can be tailored to match the design of your website. They also often provide analytics features to track the performance of your shared content.