I love Open Source!
I'm currently working on a bicycle route time planner. It uses Javascript and it's difficult to learn and program the page with the options I want at the same time (I didn't know Javascript before this). So it was very nice to come across and Javascript interpreter called SpiderMonkey Javascript engine. I downloaded it, compiled and I've been using it to write Javascript code that is used on my planner page. The great thing is that I can write experimental code and test it on the Javascript interpreter without having to reload the web page. This helps to speed up the development time tremendously. The cost to use the interpreter, the time to download and compile. My best method of repaying the Open Source community is to give back code to the community (and to find bugs and fix them). In return most of my code is also Open Source.