What is the original Io game?

What is the original Io game? The first game I discovered was Vertix.io, a charming online, nearly top down shooter that sees players dropped into a maze of concrete corridors, set to gun down any enemies they run into along the way.

The first game I discovered was Vertix.io, a charming online, nearly top down shooter that sees players dropped into a maze of concrete corridors, set to gun down any enemies they run into along the way.
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