http://www.ollydbg.de/download.htm
Registration
This software is a shareware. To use this program on a permanent basis or for commercial purposes, you should register it by sending filled registration form to [email protected]. The registration is free of charge and assumes no financial or other obligations from either side - just be fair and let me know that you like this software. Even your personal data in the registration form is optional (use your nickname or pseudonym if you want).
If you use OllyDbg together with Randall Hyde's HLA (High Level Assembly), you don't need (but still allowed) to register.
When registering, you can subscribe for information (email) on the new versions of this program, including pricing, terms of support and list of new features. In this case you agree not to treat this information as a spam as long as number of letters does not exceed 4 each calendar year and they contain no advertisements from the third parties. If you no longer want to receive this information - well, just let me know, and I will immediately delete your address from my database.
Fair use
Many software manufacturers explicitly disallow you any attempts of disassembling, decompilation, reverse engineering or modification of their programs. This restriction also covers all third-party dynamic-link libraries your application may use, including system libraries. If you have any doubts, contact the owner of copyright. The so called „fair use" clause can be misleading. You may want to discuss whether it applies in your case with competent lawyer.