A fast, (almost) garbage-free debug overlay for Unity with three components: a debug overlay, a console, and a CVar system.

Garbage is minimized by avoiding string allocation — formatting uses C#-style format strings ("This: {0}") backed by a procedural renderer with no mesh allocation.

Displays text, graphs, and primitives that update every frame:

// FPS in top left corner
DebugOverlay.Write(1, 0, "FPS:{0,6:###.##}", 1.0f / Time.deltaTime);

// Line graph of FPS below
fpsHistory[Time.frameCount % fpsHistory.Length] = 1.0f / Time.deltaTime;
DebugOverlay.DrawGraph(1, 1, 9, 1.5f, fpsHistory, Time.frameCount % fpsHistory.Length, Color.green);

Additional drawing calls: DrawHist, DrawRect, DrawLine, DrawQuad, DrawTexturedQuad, SetColor, SetOrigin. Text supports inline color markup via ^RGB (e.g. ^F00 for red).

Toggle with F12. Supports command history (up/down), tab completion, and mouse scroll.

Game.console.AddCommand("quit", CmdQuit, "Quit game");

void CmdQuit(string[] args)
{
    Game.console.Write("Goodbye\n");
    Application.Quit();
}

Built-in commands: help, dump (scene hierarchy), cvars, watch.

Typed config variables readable and settable from the console at runtime:

static CVarFloat showFps = new CVarFloat("showfps", 0, "Show FPS counter");

// In update:
if (showFps.value > 0)
    DebugOverlay.Write(1, 0, "FPS:{0,6:###.##}", 1.0f / Time.deltaTime);

In the console: type showfps to read, showfps 1 to set. Use watch showfps to display it on the overlay continuously. Types supported: CVarFloat, CVarInt, CVarString.