The GPL doesn't explicitly forbid commercial use, but as /u/tedivm points out, it often has the effect of at least strongly discouraging commercial use. That may actually be enough for what the parent poster wants. Or not... but it's worth talking about.
> Yeah, AGPL is the thing you want now to dissuade commercial use in SaaS.
The thing is, AGPL allows commercial use just fine, it only disallows proprietary use.
The fact that companies are dissuaded from making commercial use by being prevented from putting a proprietary moat around the software is really an indictment of those companies.
Heck, you can even make AGPL software a bit more friendly for commercial enhancements if you want by granting an exception for plugins the way some GPL software does, but those same companies would probably still be dissuaded.
Linux was sort of always the one big exception to that though. But you have a fair point that the SaaS world has changed the dynamic somewhat. That said, I don't think it's changed it that much.