The source code is apparently CC0 based on the README in their source repository: https://github.com/liberapay/liberapay.com/blob/master/README.md#license

Also their legal disclaimers are both readable and reasonable to me, that's a good sign: https://liberapay.com/about/legal

In fact, to me it looks so good that it feels like I'm missing something.

I'd be more comfortable if someone else looked at the terms of service to see if they come up with a similar conclusion. 

Regards, 

Elias