Here are diverse tools, which I originally have made for myself, but which might be useful for others too. Similar tools exist in the web elsewhere, but I have made these in my own way.
Coordinates conversion Converts latitude / longitude coordinates between three commonly used notations: 1) degrees, minutes & seconds (DMS), 2) decimal degrees, 3) integer degrees and decimal minutes.
Distance calculation Calculates of the distance between 2 locations with known latitude/longitude coordinates
Colour definition tool This colour tool facilitates the task to define web page element colours, which fit to each other. It also helps to find a text colour, which is well distinguishable with a certain background colour.
Browser information Shows information of your browser and operation system
IP address to country This routine gives the country name together with the 2 and 3 character country codes defined in ISO 3166-1 for a given IP (IPV4) address.
Day of the week for a date Ever wondered which day of week you were born or which day of week will the first of January two years from now be? This is a tool to show it to you.