iMessage Alternative for OSX El Capitan, with iMessaging I've been having problems with iMessaging on my Macbook Pro (iCloud account issues, which Apple support hasn't been able to fix over three support calls) for over a year.  I really need to send texts and iMessages from my laptop (it works on my iPhone and iPad fine).  Is there a non-Apple application I can use for this?  I can see multiple reasons why one would not exist, but I thought I should ask.  Thanks!
Mac is a closed system, and Apple takes many safety precautions to ensure that it stays that way, and that nothing is tampered with. Though there are indeed many ways, they all come with a consequence. My advice would be to schedule your Mac for an appointment at the nearest Apple Store and have them take a closer look at it. To schedule an appointment, you can either call in or go to their website apple.com/retail/geniusbar and follow the steps accordingly to your problem. This is the best way to get everything set back to normal.