I have every now and then done some push-hand style aikido w/ like minded folks - starting from a neutral and no defined uke/nage role, each looking for an opening/chance to take kuzushi. Requires people to be able to stay very focussed, relaxed and connected or it just devolves into a shoving match - which is a very good reality test in and of itself.
I adored doing hand-randori when I was training Tomiki. Both sides touch hands, one palm up, one down, and trade simple attacks. Point being to stick to your opponent and use the energy of the attack to pin, choke, or throw. It could turn into a shoving match with lower-level guys but with good people--my sensei for one--using any muscle at all got you into a world of hurt every time.