I got annoyed by all the temperature conversion tools that drift of into a discussion about the (trivial) formula for converting Fahrenheit to Celsius and vice versa, included ads, etc. Moreover, I wanted to have a slider for playing around with different values (e.g., to configure an A/C unit) without typing.

-17.8 °C
0 °F
100 °C
212 °F
°C
°F