This is great news, and should really shake up the tools market. Not only is it open-source, it's released under GPL, which is a pretty radical move.
Open source load test tools have been kinda sorta OK for some time, but performance testing is the only case where commercial alternatives are pretty much universally acknowledged to be superior to open source tools. Building good performance test tools is hard. What RadView has done has instantly changed the whole scene.
I am no kind of performance test expert, but I've worked a little bit with the standard open source tools for doing that work. The next time I need one, I have no doubt that I'll reach for WebLOAD first to see how it works.