On this box you select the types of engines/platforms you want to place links. The category “Web 2.0” might be a bit wrong in the term how other tools use this. It's usually a fixed URL/Site that is used for every engine in this category.
Other tools take each site that e.g. uses the “Elgg” platform and call it there “Web 2.0”. If you call it the same, than you have more Web 2.0 sites with Search Engine Ranker than every other tool on the market.
You can Use the popup menu here to load/save selections or Check/Uncheck engines by special criteria.