I am developing a web based opensource project. I was considering the AGPL v3, but I explicitly want to prevent commercial use. Non-profit orgs are welcome to use it for free.
It seems to be a common thing in the software world, but I am looking for a pre-written license that I could use or adapt.
Any ideas where I can find such a thing? Are there accepted opensource licenses that fit this criteria?
It is not a good idea to use such a license, because it is sometimes very hard to draw the line between commercial and non-commercial, especially juridically.
However, you may check out Creative Commons licenses.
You won't find any open source licenses that prevent commercial use. That's against the spirit of open source and wouldn't fit into the definition of open source.
There cannot possibly be such a license. Forbidding the use of the source code is the exact opposite of open source. Ergo, there cannot ever possible be an open source license which has such a restriction, and a license which has such a restriction cannot ever possibly be an open source license.