CHASM.EXE

It's Monday. Talk to friends, spelunk some caves, uncover some unfathomable horrors.

In CHASM.EXE, you play as Phoebe, a PhD student desperately seeking a groundbreaking discovery to complete your research. When your best friend from the university’s caving society informs you of a strange new species found in a hidden cave system, you seize the opportunity to investigate.  But reality soon diverges...

Estimated time to complete is a ~40 minutes. Explore 15 caves and a short story. Gameplay is entirely exploration and conversing with friends -- this is closer to a visual novel than to DOOM. Features handpainted 2D characters, a full 3D soundscape, and infinite meters of spelunkable scenery.

Oh, and download the Windows version. It's less laggy.