Is there a way to message between iPad and android tablets?

[GermaineHobnob]

We have skype, which works fine but doesn't alert you that someone is texting you so you only see once you go into the app.
Is there something like whatsapp or imessage on your phone/iPad which tells you when someone has messaged you on the front screen?
DS has found whatsapp for tablet for his android tablet but you can't get it on the iPad, ARGH!

Facebook messenger

I think Viber does it too

Voxer

BlackBerry Message (BBM) too...

pretty much anything that isn't made by apple should be multi platform (they are a hardware company that want to lock you in to buy more products whereas the others are software/services companies that don't really care what you use as long as you use their services)