Short answer:

You can freely use arc42 for whatever purpose (including commercial, private, government etc.) you like without restrictions. You may not re-distribute modified versions without giving appropriate credit and sticking to the original license…

Longer answer: Creative-Commons Sharealike 4.0.

Under this license, you’re free to:

• Share: copy and redistribute the material in any medium or format
• Adapt: remix, transform, and build upon the material for any purpose, even commercially.

We, the licensors, (Peter Hruschka and Markus Meuten, the creators of req42) cannot (and surely will not) revoke these freedoms as long as you follow the license terms.

You must give appropriate credit, provide a link to the license, and indicate if changes to req42 were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.

If you remix, transform, or build upon material from arc42, you must distribute your contributions under the same license as the original.

req42 is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.