BugSeeker is a fully portable Java debugger application based on JPDA. While it only runs on JDK 1.2 or higher, it supports debugging JDK 1.1 and 1.0 applications too. The BugSeeker application is a Swing-based application that allows you to step through your program while watching threads, variables, field values, etc. To use this program you will need to have a license installed. You can obtain a license from the http://www.karmira.com/products/bugseeker2/demo.html. If you already have a license key, you don't have to reregister there.