You can download the full version, without ads, for only 1.99USD from the Windows Phone market.
• Resistor color code decoder (3-6 bands);
• Ohm’s law and Reactance calculator;
• Voltage divider;
• Resistor ratio, value/series/parallel;
• Operational amplifier;
• LED resistor calculator;
• Voltage Drop calculator;
• Filters calculator;
• Many pin-out and resources.