If you need to sketch in realtime with others remotely on your tablet, phone or whatever:
http://sketch.nur.xyz/lobby
To create a new session, just change lobby to the room name you want to create or to join
(i.e. sketch.nur.xyz/brainstorming1)
I wish to KISS, but do let me know of additional features you want
desktop
ipad
iphone
PS it's extra fun with chromecast!