There are currently 768 codes registered in the ASCL; the percentages of codes hosted on different popular sites are:

GitHub: 4.17%
SourceForge: 3.78%
Code.Google: 1.96%
Bitbucket: 0.52%

That means 11% of codes indexed by the ASCL are hosted on a public site conducive to social programming. That’s higher than the 7% from two years ago (by coincidence, almost exactly two years ago) and not unexpected, given the growth of GitHub. Fewer than 1% of ASCL codes were in GitHub two years ago (only 3 at that time — wow!); now there are 32 hosted on GitHub. For comparison, there were 14 codes on SourceForge two years ago, so while that number has doubled, the growth in use of GitHub is obviously much greater.

Though stored on sites conducive to collaboration, most of these codes are not big collaborations; the majority of codes in the ASCL in these repositories have 4 or fewer authors.

I expect the percentage of codes on such sites to grow as more people use these tools for versioning; I think those who use such tools may also be more open to sharing their codes and advertising them (via links in papers if nothing else), making them easier to find/register in the ASCL, too.