The first and easiest thing you should do is make sure that you are clearly labelled as the project's author on the website of the project as well in the source

The first and easiest thing you should do is make sure that you are clearly labelled as the project's author on the website of the project as well in the source code. If any investors get burned on this (as they probably will) you don't want them suing you alleging that you were somehow contributed to the problem. Reading up on the Apache license it seems that it requires that any attribution notices be preserved. So I do hope you put notices in your source code saying you wrote it. If you didn't, do it now. Then you should consult a lawyer that specializes in IP and general business law. You may have both a copyright and business claims against that startup. If they were stupid and removed the license or any attribution from the code when they showed it to investors, then you may have a copyright infringement claim and that can be worth a lot of money. If they were smart and adhered to the apache license, then you may have a business law claim such as tortious interference with business relationships. But this gets more complex so you really need a lawyer to figure it out. You should find one that knows both copyright and business law. I believe there are lawyers that specialize in small business cases in the software industry that know both copyright and business law. I have to warn you not to get your hopes up in terms of making money. It is very difficult to make any money from lawsuits and the experience usually ends up a money losing endeavor for both parties. But you do not have to file a suit and maybe you can take some simple steps to protect yourself. Please keep in mind that nothing here is legal advice. For actual legal advice you should consult a lawyer that knows the details of your situation.