No-CD crack is a crack/patch created in order to kill the CD protection of Re-Volt. In our case this is primarily SecuROM. This type of crack is generally considered 'Illegal' to those who do not own the official CD because of the harm it causes developers and publishers. However, it does have legal uses to those who own the official CD.
Considering Re-Volt's copyright status is also in "abandonware" state, the legal validity of using the crack without the CD is unknown at this time.