There are a number of synonyms for the phrase "in play," which typically refers to a situation where something is actively being used or engaged with. Some possible alternatives might include "active," "engaged," "operational," "live," "running," "ongoing," or "in motion." Depending on the context, other options could include "in use," "utilized," "employed," "deployed," "implemented," or "put into action." Overall, the specific synonym that is most appropriate will depend on the particular meaning and tone that the writer or speaker wishes to convey, as well as the specific context and audience for the communication.