Throwaway for obvious reasons.
I built an open source project, licensed Apache. A startup raised more than 1M based on my project and forgot to remove the links to my site. A potential investor shot me an email telling me that the startup ripped my demo and is telling investors that they own the IP.
How should I respond? Is this common practice?
If you don't want people to use your software to build a business, you should release it under a license that forbids it. (There isn't such a license but AGPL effectively accomplishes this.) If you want people to be required to mention you when they use your software, you should release it under a license that requires this. (For example, the unpopular 4-clause BSD license requires this.)
With all that said, it's still kind of a jerk move on the startup's part for them not to even contact you. But modern software is made up of many people's open source software and most of them never get any acknowledgement...