A free app for Android, by MacroPinch.

Cardiograph is a handy application to measure your heart rate. You don’t need any other device or equipment to get an accurate result. The application uses your smartphone’s built-in camera and image processing to calculate your heart rate.

This application does not require any external hardware to work, so you can begin using it as soon as the installation is finished. Each measurement that the app makes is automatically saved, allowing you to get back to it anytime you need to go through it for tracking. It can also track the heart rate data of multiple people on one device.