Evaluators’ main encounter with views of the future is in the form of theories of change, about how a programme will work to achieve a desired end, in a given context. These are typically focussed on specific relatively short-term futures, which are both desired and expected. But even in the short term, reality often involves unpredictable events which must be responded to. Other ways of thinking about the future may be helpful and complementary, notably those developed by foresight practitioners working in the field of futures studies. These pay more attention to a range of possible futures, rather than a single perspective. One way of exploring such futures is by using ParEvo.org, an online process that enables the participatory exploration of alternative futures. This article explains how the ParEvo process works, the theory informing its design, and its usage to date. Attention is given to three evaluation challenges, and methods to address them: (a) optimising exercise design, (b) analysis of immediate results and (c) identifying longer-term impacts. Two exercises undertaken by the Cambridge-based Centre for the Study of Existential Risk (CSER) in 2021–2022 are used as illustrative examples.