After months of preparation, and teasing, 
What Is Zappl?
Zappl is a short-form social media network, which allows its users to be upvoted and thus rewarded for their zappls zaps. Being based on the Steem blockchain, the platform offers easy sign-up and connection with already known peers/Steemians who can comment and upvote.
Zapplers (??? - hey, it's better than tweeple!), have the opportunity to set a title for each post, upload an image, and can use upto 240 characters. Beats Twitter's 140 (or 280), yet still nothing you want to see the Real Donald T. make use of.
The Zappl interface is still slightly nostalgic in design, and we found several minor errors like lack of retina-quality images, but all that should soon change as the mobile apps for Android and iOS launch, with a cleaner and more micro-blogging optimized design.
Zappl comes with a complete account management interface and you can even access your Steem Wallet on Zappl, which makes sense since when SMTs will be launched in 2018, not every Zappl user may also have a Steemit account. Yet, you can login with just your posting key. If you don't plan to claim rewards via Zappl, or prefer managing your wallet with the desktop Vessel wallet, you don't need to login with your active or master key.
As can be seen in the screenshot of the (desktop) browser UI, Zappl will offer a messaging functionality to communicate with other Steemians/Zapplrs. At the time of writing that functionality was still 'Coming soon' though. For now, if you really think you deserve that much attention, and don't want to use chat/Discord, you will still have to send a minimal fee and include your message with a financial transfer. Or use busy.org.
The clean Zappl editor
While it rests to be seen whether Steemians will adopt to the format, or Zappl will soon be the "Horror of Everything Bucket Steemit", which shows each zap as a normal post, rests to be seen.
Personally, we think that there is a bright future for a platform like Zappl, although the question of whether its eventual coin/currency will attract investors and invite stability is a serious one. Looking at counterpart Twitter, and its inability to convince advertisers to spend more on the platform, it is obvious that just Tweets don't cut it. Long term, especially after a possible ICO as SMT built on the Steem platform, this will be an intriguing question to answer and probably problem to solve.
Until then, we look forward to seeing how Zappl will grow and whether it will find a foothold in specific niches like Mastodon has, or just be a mainstream rather generalist Twitter on $teroids.
As the tune usually goes... follow us maybe and congrats to 
pl that!
Update
As per Zappl's post the platform will be offline a little for some bugfixing.
Update 2
Zappl Beta has now launched, as per its latest post.