It's out on Steam on 2nd September http://store.steampowered.com/app/517710/

You can pre-order it cheaper on Humble Bundle: https://www.humblebundle.com/store/redout

Other interesting future racers on Steam include:
Bank Limit: http://store.steampowered.com/app/493500/
Radial-G: http://store.steampowered.com/app/330770/