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Songmics Small Pet Playpen (Amazon)

Why the heck is this item here?  The plastic panels can be reconfigured to construct a clear barrier if you need to separate cats during an introduction process, etc.!  It’s a great alternative to expensive and awkward baby gates, and can be built in several different sizes to accommodate doorways, entrances, etc.  Use zip-ties and screw-hooks to secure, and use it like a door.