Ethereum is a public blockchain / cryptocurrency platform for building decentralized web applications and financial / social technologies.
The developers and wider community behind this website are generally forward-thinking, intelligent, and friendly.
I believe the claims on the site are accurate, trustworthy, and speculative in nature.
I've found the software made available through the site to be secure and reliable.
Source: testimonial based on 2 years experience.
The site provides a way to develop applications like bitcoin provides a way to trade. It's decentralized and independent, the programs made are distributed over thousands of computers, instead of being on a single server.
Ethereum is a next-generation cryptocurrency platform that allows you to create any kind of smart contract or decentralized application that you can imagine.