The first great series to showcase on Newgrounds. Still a favorite!
A security guard is trapped in a bunker, with a strange creature crawling around.
Mythological creatures share a New Jersey apartment together. Hilarity ensues.
While a majority of web games from 1998-2009 were made with the Adobe Flash IDE, the SWF format has since become open and a variety of frameworks and tools have emerged (many of them free) to facilitate game development! If you're interested in any of these platforms, here is a place to sample games made with each one.