My Kobo H2O modifications:
Perform patches directly on the Kobo. Beta stage. Unfinished. http://www.mobileread.com/forums/showthread.php?t=253265
Create collections for each folder directly on the Kobo. http://www.mobileread.com/forums/showthread.php?t=254554
Study flashcard / spaced repetition while you read. https://www.mobileread.com/forums/showthread.php?t=311894
Move all hyphenation dictionaries to USB storage /.addons/hyphendicts/ for editing. http://www.mobileread.com/forums/showthread.php?t=266005
Upgrade/Replace the Kobo's internal SD card on the fly. http://www.mobileread.com/forums/showthread.php?t=261578
Display current date/time on screen. https://www.mobileread.com/forums/showthread.php?p=3762123#post3762123
Modify PNG images embedded in the nickel binary. http://www.mobileread.com/forums/showthread.php?t=262837
Display a random screensaver PNG image on standby/poweroff. http://www.mobileread.com/forums/showthread.php?t=255238
Enable telnet and ftp servers. Survives most firmware updates.
Show whether user partition was properly umounted for USB export. http://www.mobileread.com/forums/showthread.php?t=263674
A local web server running on the Kobo and the things you can do with it. Also includes a hack that allows intranet wifi usage (without WWW access). http://www.mobileread.com/forums/showthread.php?t=262353
Add support for ext2/3/4 filesystems for USB and SD storage. http://www.mobileread.com/forums/showthread.php?p=3003110#post3003110
Kobo <-> Win10 compatibility hack. http://www.mobileread.com/forums/showthread.php?p=3367786#post3367786
A program that draws PNG image data on the display, regardless of rotation. DISCONTINUED: Use https://github.com/NiLuJe/FBInk instead.