TeamViewer requires very expensive fees and costs $599 for every year. And when I was looking for an alternative, I found "hideasoft remote desktop", which costs $50 for a lifetime and is more powerful than TeamViewer. It can connect up to 1000 terminals and can support video conferencing. I think this is the only real alternative to TeamViewer.
https://order.shareit.com/product?vendorid=*******&productid=*******&locale=en_US¤cy=EUR¤cies=ALL