These are all listed in absolutely no order..
Bowser frames lets you look at bowser frames for different framerules, to determine the difficulty of a given 8-4 entrance framerule.
This practise rom builder adds level select and sockfolder information to relatively basic SMB1 romhacks.
5-4 good bars for small mario is a way to adjust the rotation of firebars in 5-4 to get good bars as small mario or small fire mario while losing a minimal amount of time.
I also have some smb related things up on github, mostly source for some little hacks.
There's this picture of 1-1 and 4-1 fpg right release locations to ensure good subpixels, and also a similar little helping image for BBG positioning. Not sure they'll make sense to anyone but me, but you're free to look at them.
Here is the small fire warpless spreadsheet that I made. The idea is that your 0.0 reference splits are on a straight line across the sheet, then as you gain or lose time you go up/down the sheet one step per framerule.
You might enjoy exploring the glitched worlds of Super Mario Bros, there are some weird things hidden away in there! Kosmic has a video showing it off a bit which is a fun watch!