Xtra ZAP is a free online service. It provides various tools without any cost, forever. You can use this tool for your benefit without any hesitation.
For now we do not offer any such service for signup and login. This might change in near future depending on the user's demand.
Yes, this is a totally free service. You are not required to pay anything if you want to utilize these services.
There are a lot of tools/services in pipeline which will be added gradually in the future.