Where can I find space-time calculators online?

I’m looking for information specific to two areas. First, I’m looking for information on current space vehicle speed and potential speeds attainable within the next 20–50 years using technologies on the horizon. For example, ion drives gradually increase speed over time. But what speed do they start at? Is there a maximum speed attainable? What is the rate of acceleration? Is there a chart or something for quick reference to gather this information and compare space travel technologies?

Secondly, I’m looking for a calculator where I can input data such as speed (velocity) and length of time of travel to calculate time relative to Earth observation and the traveler. For example, I want to calculate time differences for an Earth observer and a traveler that leaves Earth orbit at a specific velocity (say 50% the speed of light) and travels for 10 years round trip. Obviously, the traveler is 10 years older, but how much time has elapsed on Earth? Anyone know of an online calculator of this type that I can play with?