WaveThis is a web service that allows you to quickly start a discussion on Google Wave using the content of any website. WaveThis provides both a URL format for initiating that discussion, and a UI widget that you can place on your website to start a discussion in Google Wave.
If you are here because you simply want to use WaveThis to share content from your favorite sites, you can use it in two main ways:
Both of these work in the same way - select the text that interests you on the page, and click the icon or bookmarklet. A new wave will be created with the content and link to the original page, and you can share that wave with others.
If you are a developer and want to use WaveThis in your site, read through the Developer's Guide.