Once you install Everdo, it creates a local database for your data. That data never leaves your computer, which is the best privacy and security measure ever.
Because your GTD system is an extension of your brain and it doesn't make sense to upload it somewhere else if you don't have to.
Cloud-based apps store your data on third-party servers in clear-text, unencrypted form. This is done in order to provide a seamless experience and some features (like search) which are impossible on encrypted data. This is an additional risk you don't need to take. Everdo eliminates it by being a local, offline app.
Everdo does not delete your actions and projects, except the trash you destroy yourself. This means you'll be able to look up anything you ever did at some point in the past.
SQLite is an open-source file-based database format. This makes your data always available and open to you, so you can do whatever you want with it:
You can learn about the database schema and location on the forum.