The most important things you need to know are

1. everything in 2sxc is open source and free
2. 2sxc itself is licensed under the extremely permissive MIT license
3. 2sxc contains many, many other third party components which are also open source.
1. The licenses used range from AGPL (very copyleft) to X11 (aka MIT, very free).
2. Most of the components use very permissive licenses (like MIT or Apache 2.0)
3. A few components contain copyleft requirements - this is especially relevant for the Image Resizer

So in summary: if you want to create open-source work, you can stop reading now - or just donate something for a good cause. If you don't want to share your work with others, please read on...