Both are interest-separated discussion boards. Reddit bills itself as more news-oriented, but quite often it serves as a regular threaded forum where the first post sets the context.
After reddit got big, we started seeing (well, started speculating that we're seeing) a lot of people come to 4chan after initially cutting their internet discussion teeth on reddit. There were speculations of a secret irc cabal of redditors, who collude to drive threads offtopic and in general mould board culture to be more reddit-like. To this day I'm not sure if those allegations were insubstantiated. We did have several prominent spammers who comandeered fleets of hundreds of proxies and spammed threads they didn't like with random-generated posts. These were obviously not redditors, but given there are people who care enough and have free time enough... In short, 4chan is a magical place.
After reddit got big, we started seeing (well, started speculating that we're seeing) a lot of people come to 4chan after initially cutting their internet discussion teeth on reddit. There were speculations of a secret irc cabal of redditors, who collude to drive threads offtopic and in general mould board culture to be more reddit-like. To this day I'm not sure if those allegations were insubstantiated. We did have several prominent spammers who comandeered fleets of hundreds of proxies and spammed threads they didn't like with random-generated posts. These were obviously not redditors, but given there are people who care enough and have free time enough... In short, 4chan is a magical place.