The bar to entry was much higher, both for a project and a potential contributor. But that's not just because of no github
Projects had to find a home (sourceforge ended up a major player here) and for most, fill out some large form to be accepted. Then they had to get noticed - slashdot or similar, since there was very little "social" effect on the project host.
When a project did try to get noticed, it had to already be "good" enough to get people interested. Practically nobody would stumble on a half-implemented tool, because there was nowhere to stumble there from. And it wouldn't get the push and discussion on newsgroups or websites if it was half-implemented.
Contributors had to first find the active developers. Many times, that was not on the issues list or a newsgroup, but on an irc channel mentioned in passing in a readme file or on a newsgroup ("I was talking to bud on #ourproj about the thread scheduler..."). Once you found them, you could try to "break in".
Since 95% of the OSS projects you'd actually find were already "good enough", that meant there were already a good number of active contributors that had formed a clique and were understandably protective. In many cases, you had to work hard to get them to accept that you might help rather than be a burden. That meant hanging out on irc or newsgroups and trying to impress.
Once a project was abandoned, there was nearly no way to contribute, you'd have to fork it. Unfortunately, your fork would have to beat the searchability of the original project with even more buzz, or people would find the abandoned one and have no inkling that your fork existed.
Obviously this is an over-generalization... there's no way to really encompass how all OSS was, even if I knew -and many major OSS projects were not at all like this, since each had it's own ecosystem and quirks.
In general the discovery of projects, and the ability to contribute, has grown in leaps and bounds around the time of github. But that is due also (to a very large extent) to other tools such as blogs, social sites, news sites (eg hacker news), and better search with google. Really, github is just a part of a huge increase in online interaction between people.