TwlNmenu is the name for an application that comes bundled with Nintendo DSi SDK's, also known as Panda DSi's by the community. This application would install *.TAD files, an installable archive developed by Nintendo, similar to RocketRobz's cancelled *.TIA file format.
First surface
The existance of NandFiler and TwlNmenu was discovered at Gamescom 2009 when users by the name of Demo and Shadowchao started discussions about 2 development apps. Unfortunatly, both were unable to open the applications, because there was security walking around and the Nintendo DSi unit was hooked up to a monitor. Fast-forwarding to Febuary 11th, 2013, a collector by the name of LimboFunk mentioned a Nintendo DSi Development Unit, as well as the correct names for the applications. There wasn't much discussion after that, except for references, with no dumps being made. However, on September 2nd, 2017, a TWLSDK was leaked containing WMTestTool, RelayStation, modified versions of DS Download Play named MB_Child and Rev. 11364 of NandFiler and TwlNMenu.