While unsigned arithmetic is not "enabled by-default", a simple `import unsigned` and you have it.
If you want the language to handle overflows for you, you can enable runtime overflow checks for your whole code or any specific part of it.
Otherwise, if you opt for no runtime checks and release builds with all optimizations, you indeed go into the same undefined behaviour territority as in C, so you'd have to prevent overflows before they happen.
Well, it was named "Nimrod" before, but there were other problems with that name, which prompted the rename. "Nim" was a good choice because it was the file ending already. Also, easier to google than C and Go at least. Usually "nim-lang" works fine.