Many calculators from Fluid Mechanics (physics/engineering), including:
Absolute Pressure
Bernoulli Theorem
Brake Horsepower
Bulk Modulus
Compressibility
Head Loss
Flow Rate
Fluid Density
Fluid Pressure
Fluid & Flow Velocity
Net Positive Suction Head & Cavitation
Pump Efficiency
Specific Gravity
Stokes Law
Water Horsepower