Flappux is described as 'HTML based clone of Flappy Birds that is unapologetically free software'. There are more than 25 games similar to Flappux for a variety of platforms, including Android, Android Tablet, Online / Web-based, iPhone and Windows Phone. The best alternative is Twisty Leaf, which is free. Other Flappux like games are A7X Flap (Free), Tipsy Bat (Paid), FlappyLearning (Free, Open Source) and Flappy Bird Online (Free).
Tipsy Bat is a Flappy Bird game with a VR twist. Your view follows a woozy bat in a circular radius, guiding and keeping him from hitting obstacles. Controls are simple though you'll need to ensure you can keep turning in a circle while playing.
In Tricky Sky you must fly as far as you can while avoiding the bats. Catch the right flow, and maybe you'll get through the tricky sky. Be sure to collect some gems on the way, to unlock new birds and planes! Or just pick up a star, and become invincible.