This post has information useful for those using the 1.9 beta.
Andrew decided to call the new inputs system I cooked up "funky trees". Somehow escapes me why, but I'll roll with it. Here I'll describe what you can do in the land of funk.

First, you can do everything you used to be able to. The new system will only be activated if the input doesn't fit the old system, so all old builds should remain functional.

Inputs

What you can now do is use the normal input axes:

• Pitch
• Roll
• Yaw
• Throttle
• Brake
• Trim
• VTOL
• LandingGear
• FireGuns
• FireWeapons
• LaunchCountermeasures
• Activate1
• Activate2
• Activate3
• Activate4
• Activate5
• Activate6
• Activate7
• Activate8

Flight data

In addition to this you can access some information from the aircraft:

• Altitude - Aircraft's altitude in metres
• AltitudeAgl - Aircraft's altitude above ground level in metres
• GS - The speed relative to the ground (m/s)
• IAS - The speed relative to the air, adjusted for the desnity of the air (m/s)
• TAS - The speed relative to the air (m/s)
• Fuel - The amount of fuel remaining as a proportion of capacity (0 to 1)
• AngleOfAttack - The angle of attack (angle airflow vertically meets the boresight) in degrees
• AngleOfSlip - The horizontal equivalent of angle of attack (degrees)
• PitchAngle - The pitch of the aircraft (degrees)
• RollAngle - The roll of the aircraft (degrees)
• Heading - The heading of the aircraft (degrees)
• Time - The time since the level loaded (seconds)
• GForce - The acceleration and gravitational "force" acting on the cockpit in G. I know it's not a force. Shut up.
• VerticalG - The signed vertical component of the "G Force".
• SelectedWeaponName - The name of the selected weapon
• Latitude - The North/South position of the craft (metres)
• Longitude - The East/West position of the craft (metres)
• PitchRate - The pitch angular velocity in degrees/second
• YawRate - The yaw angular velocity in degrees/second
• RollRate - The roll angular velocity in degrees/second (these 3 inputs are better than using rate(PitchAngle) etc, because they account for wrapping around the angle, as well as being in local space: rate(Heading) is different to YawRate)

Constants

Values that are always the same:

• pi the mathematical constant pi (half a tau, if you will).
• e the mathematical constant e.
• true a true boolean value
• false a false boolean value

Operators

These are useful for... maths or something.

• Mathematical:
  
  
  
  • +, - addition and subtraction (- can be used as a unary operator, for instance -Pitch
  
  
  • *, / multiplication and division
  
  
• Comparison:
  
  
  
  • <, > less than, greater than
  
  
  • <=, >= less than or equal to, greater than or equal to
  
  
  • ==, != equal to, not equal to
  
  
• Boolean:
  
  
  
  • &, AND
  
  
  • |, OR
  
  
  • !, NOT (this is a unary operator)
  
  
  • Ternary operator: condition ? value_if_true : value_if_false - this chooses between two values based on the condition.
  
  

Functions

Finally, there's some helpful functions to do maths for you!

• abs(x) - The absolute (positive) value of x.
• ceil(x) - x rounded up to an integer.
• clamp(x, min, max) - x clamped between min and max.
• clamp01(x) - Equivalent to clamp(x, 0, 1).
• deltaangle(a, b) - The shortest angle delta between angles a and b in degrees.
• exp(x) - Returns e raised to the power of x.
• floor(x) - x rounded down to an integer.
• inverselerp(a, b, x) - Calculates the linear parameter t that produces the interpolant value within the range [a, b].
• lerp(a, b, t) - Linearly interpolates between a and b, by a proportion of t.
• lerpangle(a, b, t) - Similar to lerp, but interpolates correctly when values pass 360 degrees.
• lerpunclamped(a, b, t) - Similar to lerp, but doesn't clamp the value between a and b.
• log(x, p) - The logarithm of x in base p.
• log10(x) - Equivalent to log(x, 10).
• pingpong(x, l) - "Ping-pongs" the value x so it is never larger than l and never less than 0.
• max(a, b) - The largest value between a and b.
• min(a, b) - The smallest value between a and b.
• pow(x, p) - x raised to the power of p.
• repeat(x, l) - Loops the value x so it is never larger than l and never less than 0.
• round(x) - Rounds x to the nearest integer.
• sign(x) - The sign of x (1 if x positive, -1 if x negative)
• smoothstep(a, b, t) - Similar to lerp, but with smoothing at the ends.
• sqrt(x) - The square root of x.
• sin(x) - The sine of x (degrees)
• cos(x) - The cosine of x (degrees)
• tan(x) - The tangent of x (degrees)
• asin(x) - The arc-sine of x (degrees)
• acos(x) - The arc-cosine of x (degrees)
• atan(x) - The arc-tangent of x (degrees)

Memory Functions

These are functions that are special because their output not only depends on inputs but their previous state.
- sum(x) - Returns the sum of all it's inputs over time (the integral of x)
- rate(x) - Returns the rate of change of x relative to its value last frame (the derivative of x)
- smooth(x, t) - When loaded, it's output is set to x. As x changes, the output tries to move to x, but at a rate of no greater than t. This is vaguely equivalent to changing the speed of a rotator.
- PID(target, current, p, i , d) - Evaluates a PID controller with the setpoint of "target", process variable "current" and the gains p, i, and d. Equivalent to: p * (target - current) + i * sum(target - current) - d * rate(current)

With all of these at your disposal, I'm excited to see what kind of contraptions you guys come up with, and I'm also open to some suggestions as to some things that could be added.

-WNP78, your funk master.