About OpenWhatsapp: OpenWhatsapp is a chat client for mobile platforms which uses the WhatsApp service. You can use OpenWhatsapp to communicate with any of your friends who use WhatsApp. This includes group conversations, sharing images, videos, music, contacts and even your locaiton. In other words, whatever WhatsApp does, OpenWhatsapp can do.
The entire OpenWhatsapp project was created when WhatsApp originally stated that they were not bringing their app to BlackBerry 10. It took off from there and became a big contender as an open source project. Since then, WhatsApp has verified they are coming to BlackBerry 10 - expected to release this month. However, the OpenWhatsapp project will still continue.
The developers have stated that there is a release v0.9.2.5 for Blackberry Z10 awaiting approval in BlackBerry World. But if you want, you can still sign up for their early testing program to get the app before it hits the storefront.
Sign up for the OpenWhatsapp early testing program, and get more details on the OpenWhatsapp website.