dP100 Lite is a pressure drop calculator (for vapors only) that calculates the pressure drop for vapors assuming 100 ft. of the line size you entered--in an annular space. The full version also has included some notes providing you with examples of the roughness factor of the pipe, some details on the friction factor equation used, and a pipe table showing you various inner diameters for different pipe sizes, and their corresponding pipe designations (e.g., standard wall, sch. 40, sch. 80).
The full (paid) version includes: liquid calculations (input SCFH or actual CFH); annular flow dP/100 (for both liquid and vapor); equivlanet diameter calculation. Also, for vapor input, you can input just the T , P, and MW and it will calculate density for you, and try and estimate the viscosity (rough correlation on viscosity though).