Alma Mater, St George's West, Edinburgh (4/5)<br/>You Once Said Yes, Underbelly, Edinburgh (3/5)

The play for one is becoming a Fringe staple, which is strange but heartening in these economically straitened times. Pushing at the boundaries of what theatre can be, such plays may not represent the best value for money for producers, but for privileged audience members they are often among the most memorable experiences.

This year, in a Fringe first, the experimental Glasgow duo Fish and Game are presenting a play on an iPad. Or is Alma Mater a play? It is somewhere between theatre, film and art installation, really. You are given headphones and an iPad and ushered into a crate. The door closes and you find yourself in a child's bedroom which, thanks to the gadget in your hands, gradually fills with a cast of characters. Except when you look up, you are all alone.

It is eerie, unsettling and very, very clever. Early on, a pair of shoes appears magically, under a chair. The format encourages us to look at the world from the perspective of two children – we watch their games, see their tears and laughter, enter their imagination and their nightmares as a classical score plays. If the loose narrative rather loses its way in the last five minutes, it is better to succumb to the dream-like mood. This is a bewitching 20-minute encounter that stays with you long after you hand back the iPad.

You Once Said Yes requires more active engagement. Starting at the Underbelly, you are stripped of your possessions, given a waterproof poncho and a bag containing a rose, a wallet and a Waitrose receipt and sent out on to the street, where you are immediately accosted by a backpacker who can't speak English. So long as you go with the flow and, crucially, keep saying yes, you'll get there in the end.

Without giving too much away, the play – written by by Morgan Lloyd Malcolm (whose Belongings just transferred from the Hampstead Theatre Downstairs) and Katie Lyons – is a series of encounters with characters dotted around the city. You'll meet a harried lawyer outside the courts, a lonely clown on the Royal Mile and a homeless man on Grassmarket, to name just a few.

I loved it for how it opened my eyes to places I had never seen and for its feelgood ending. But the monologues, about the dilemmas and decisions of everyday life, were rather trite and drawn out. En Route took a similar mystery tour last year and, I think, made the same point about personal liberation in a less heavy-handed way. But this is fun nonetheless.

'Alma Mater': to 29 August (shows start every 10 mins from 11am to 6.50pm) (0131 226 0000). 'You Once Said Yes': to 29 August (shows start every 10 minutes from 12.30pm to 2.50pm) (0844 545 8252)