555 Timer Free is a calculator to help you with your work, with 3 astable modes and monostable mode. Astable modes include duty cycle less than 50%, duty cycle equals 50% and duty cycle greater than 50%. Resistor and capacitor values can be tweaked.
1. 3 astable modes
2. monostable (one-shot) mode
3. duty cycle indicator
4. can tweak R & C values

The license of this software is Freeware, you can free download and free use this calculator software.