TOPCAT is similar to real-life software and was developed by professional airline pilots.

Features
Microsoft Windows application made by professional airline pilots (does not require any other software)
Easy-to-use, user-friendly interface resembling real-life software
Worldwide database with close to 10,000 airports and 28,000 runways
Including obstacle data and engine-out procedures (EOSIDs)
Take-off and landing data for abnormal configuration (e.g. engine out, flapless landing, inoperative thrust reversers, etc.)
Ready-to-print and ready-to-save loadsheet, take-off and landing reports
Build your own Individual Runway Tables (IRTs) for your favourite airports
NOAA, IVAO, VATSIM and ActiveSky weather support (FS2004 and FSX)
A wide variety of units: kilograms (kg), pounds (lb), meter (m), feet (ft), hPa (hecto pascal), inHg (Inches of mercury) for your personal needs
Editor to add or modify runways and airports