The standard distribution ships with the following tools:
Hot code reloading
The "Hot code reloading" feature is built into the compiler but has its own document explaining how it works.
Documentation generator
The builtin document generator nim doc generates HTML documentation from .nim source files.
Nimsuggest for IDE support
Through the nimsuggest tool, any IDE can query a .nim source file and obtain useful information like the definition of symbols or suggestions for completion.
C2nim
C to Nim source converter. Translates C header files to Nim.
niminst
niminst is a tool to generate an installer for a Nim program.
nimgrep
Nim search and replace utility.
nimpretty
nimpretty is a Nim source code beautifier, to format code according to the official style guide.
testament
testament is an advanced automatic unittests runner for Nim tests, is used for the development of Nim itself, offers process isolation for your tests, it can generate statistics about test cases, supports multiple targets (C, JS, etc), simulated Dry-Runs, has logging, can generate HTML reports, skip tests from a file, and more, so can be useful to run your tests, even the most complex ones.