It's not how simple the product is or whether it's open source that determines regulatory requirements, but what it is and where and to whom you're selling it.
For a quick primer on FCC requirements (which only covers US EMC), check out Sparkfun's "The FCC and Open Source"[1]. For more depth on other regulatory requirements, e.g. safety, "Global Certifications for Makers and Hardware Startups"[2] is pretty decent.