| npmignore | NPM Ignore |
| nqc | Not Quite C Source Code |
| nse | Nmap Scripting Engine Script |
| nsh | NSIS Header |
| nsi | NSIS Script File |
| nsis | NSIS Script File |
| nuke | NUKE Script |
| nunj | Nunjucks Template |
| nunjs | Nunjucks Template |
| nunjucks | Nunjucks Template |
| nupkg | NuGet Package |
| nuspec | NuGet Specification Data |
| nut | Squirrel Source Code |
| nvb | NVSG SDK Scene Graph |
| nvv | Nvidia Vertex Shader Profile |
| nw | Sweave Document |
| nxb | C4 Engine Binary Model Data |
| nxc | Not eXactly C Source Code |
| nxd | AdaOS Debugging Information |
| nxg | eSite Builder NXG Web Page |
| nxu | C4 Engine XML Model Data |
| o | Compiled Object File |
| oat | Android Compiled OAT |
| ob2 | Oberon 2 Source Code |
| obak | WinSQL Offline Backup Data |
| obe | Objeck Executable File |
| obh | Hitachi Ladder Editor Object Program |
| obj | Compiled Object File |
| obl | Objeck Compiled Library |
| obn | Oberon 2 Module Source Code |
| obr | Borland C++ Object Browser Data |
| obs | Objeck Source Code |
| obs | ObjectScript Script |
| obv | ObjectScript Form |
| oc | Esterel Compiler Automaton Code |