Substrate

Recursive tower defense. You can place chips, and each chip has another map inside it that you also have to defend. Enemies that get through an inner map come out on the higher level with more health, so building deep is a risk.

Controls

- Left click: build, or select a building

- Right click or Esc: cancel, clear selection

- Right or middle drag, WASD: move the camera

- Mouse wheel: zoom; scroll over a chip to go inside

- Double-click a chip or Enter: fly into it

- Backspace or Z: zoom out to the board above

- H: back to the surface. Tab: next board

- Space: start the next wave (early for bonus energy)

- F: game speed. P: pause

- 1 to 7: towers. Q / E / C: wall / extractor / chip

- U / X / T: upgrade / sell / change target

- B: purge, then click where it should hit