I just wanted to make a list of the best and most important programs for the NSMB hacking and here it is.
a note in advance: I own neither the rights to the programs, nor do I know all the programs completely, so if I make mistakes or forget a program tell me.
The download liks and the sources are at the bottom of the post
and without further ado, here is the list.

Editors:
NSMB Editor

This is the most important tool for the NSMB hacking, because with this program it is possible to edit, extract and replace levels, tilesets, backgrounds and other graphics and files. The editor is also there for ASM hacks, more specifically, to insert the code


File Converter:
Midi2sseq
Converts midi files to sseq files.

sseq2midi
a program to convert sseq`s to midi`s. good to make midi's out of the sseq's from other DS games. (This is also possible with other programs)

I'm just taking these two of several converters, the reason why I'm only taking these two because the midi2sseq.rar contains the necessary .dll files for looping and a Command Prompt application, which is important if you want to loop the sseq`s and because of the MKDS Course Modifier or the Every File Explorer can convert most of these files. I took sseq2midi because, in my opinion, it's better than just exporting the midi's with VGMTrans. a tutorial on how to convert midis with the command prommt program can be found here: https://www.dshack.org/forum.php?page=thread&tid=315


File Viewer/File Extractors:
NDS_Editor
MKDS Course Modifier
Every File Explorer

With these tools it is possible to extract, view and edit files from a ds rom
(with Every File Explore it is even possible to add files).


Graphic Tools:
PhotoFiltre, Photoshop, Gimp, Paint.net etc.
To edit the graphics

MKDS Course Modifier
Every File Explorer
To view and replace the files

3D Modeling Tools like Blender
To edit 3D graphics


Music Tools:
NitroStudio
probably the best program to edit the .sdat! with this program it is possible to add new songs soundbanks etc. to the .sdat, to change the names of the files, to edit the files, to create your own .sdat. Import, Export, replace files, and more.

DSSoundStudio
Apart from adding files to .sdat, editing files and converting files, this program has similar or the same functions as the NitroStudio.
(this information will not be completely accurate)

VGMTrans
With this program it is possible to extract the .sseq, .sbnk and .swar files from DS games. It is also possible to convert .sseq`s into .mid (midi) files, .sbnk`s into .dls files and .swar into .wav files. You can also listen to the sseq`s.

Audacity
For editing .wav files.

FLSTudio
With FL Studio you can use the .dls files extracted from the game with VGMTrans to test how your midi would sound in the game. Also you can change the instruments of your midi`s with FL Studio so that it sounds good in the game (or that you can hear something at all).

Anvil Studio
With Anvil Studio you can set the instruments like they are in FLStudio.

Cakewalk Studio
To set the "loopStart" and "loopEnd" events.


Programming/ASM Hacking:
DevKitPro
HexWorkshop/Hexeditor


Emulators (For testing your hack):
DeSmuME

Flashkarts:
perfect to test your hack on an original DS / DSI / 3DS

melonDS:
an emulator that supports local multiplayer. Good for testing MvsL hacks.


Other:
Save Editor Tool:

Titlescreen Editor:
A title screen editor that converts .png files so you can use them as a title screen image. Template is already included

Worldmap Editor:
An open source world map editor, for NSMB DS from RicBent.
With this editor it is possible to edit the paths, each frame of the path animations and the visible nodes on the World Map.

Zoom sprite helper:


AdressHelper
This Tool converts the addresses in IDA to the ones where the code ends up in memory while ingame and vice versa.
(original post: https://nsmbhd.net/thread/3858-tool-address-helper/)


Sources:
https://nsmbhd.net/thread/4252-nitro-studio/
https://devkitpro.org/
http://www.hexworkshop.com/
https://www.image-line.com/flstudio/
http://anvilstudio.com/
https://nsmbhd.net/
http://www.photofiltre-studio.com/news-en.htm
https://www.adobe.com/de/products/photoshop.html
https://www.gimp.org/
https://www.getpaint.net/index.html
https://sites.google.com/site/kiwids/
https://www.dshack.org/forum.php?page=thread&tid=315
http://melonds.kuribo64.net/downloads.php
https://nsmbhd.net/thread/3858-tool-address-helper/
https://nsmbhd.net/thread/2064-nsmb-titlescreen-editor/
https://nsmbhd.net/thread/4220-save-editor-tool/
https://nsmbhd.net/thread/2821-zoom-sprite-helper-download/
http://desmume.org/download/
https://nsmbhd.net/thread/2585-useful-stuff-for-nsmb-hacking/
https://drive.google.com/file/d/0B9ZYBSGvTGbiQ1A2Wmh1YnVaRjA/view

Now have Fun
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Official DSX YouTube Channel
F-Zero DSX on Twitter
The F-Zero DSX Discord Server

You might want to be reminded that the same thing was done almost four years ago: https://nsmbhd.net/thread/2585-useful-stuff-for-nsmb-hacking/

It is a more detailed list too.
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Check out these awesome hacks! Beyond DS is now my major hack!

I'd add melonDS in the emulators, it's useful for MvsL hacking.
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.

You're right, I should add a few things so the list is a little more detailed and up-to-date.

Thanks for your feedback
----------------------------------------------------------------

Official DSX YouTube Channel
F-Zero DSX on Twitter
The F-Zero DSX Discord Server

Typo there https://prnt.sc/ianf9d you could also link melonDS for MVL Hacking purposes http://melonds.kuribo64.net/downloads.php