I used a customised MATE on a Raspberry Pi with touch screen. It wasn't an amazing experience, but the on-screen keyboard was reasonable. I don't know what OS

I used a customised MATE on a Raspberry Pi with touch screen. It wasn't an amazing experience, but the on-screen keyboard was reasonable. I don't know what OSK Gnome uses - it could just be a version of the same thing - but the one in Ubuntu MATE for the Pi was OnBoard.