This paper reports on two design experiments aiming to support participation in the semi-public space of an art gallery. Through 36 interviews, we analysed the collaborative production of texts about artworks both in the physical space of the art gallery and in the digital realm. In the first experiment, the prototype explicitly enabled in-situ collaborative writing, while in the second experiment the prototype enabled both in-situ and ex-situ collaborative writing. Our findings help us to better understand and further enhance the notion of participatory IT based on actual use. We analysed in-situ and ex-situ collaborative writing activities using the two prototypes, which led us to propose four new strong concepts for supporting the understanding and design of participatory IT that fosters local and remote participation linked to a semi-public space.