NDS:FlashMe
Loopy (Olimar)'s FlashMe is the best known of the custom firmwares for the DS. The current version, v8a, fully supports the DS Lite - including uninstallation.
Features
While primarily invented for the convenience of Slot-2 flashcard users as an alternative to carrying a PassMe/NoPass (and therefore of reduced value nowadays), some of the side features are still of interest:
- Optionally skipping the startup animation (with a non-stealth version).
- Accepting unsigned software over DS Download Play.
- Anti-trojan brick protection (by stuffing a basic card loader in the write protected area).
- Allowing variable brightness on all consoles capable of it.
The "noauto" variants, which omit Slot-2-as-DS booting by default, are recommended for most users.
Installation
Installation simply involves running the installer and then shorting the SL1 pad (which disables the write protection), conveniently accessible from the holes around the battery compartment after removing its cover. However, especially with the tighter packed DS Lite, care must be given to not short SL1 to other parts; this includes VR1/VR2 (the potentiometers for screen bias voltage adjustment, also accessible in the same manner). This is a likely consequence, which in turn causes the console to power off in an untimely manner.
Should it be needed, the firmware (that is part of the Wi-Fi card) can be either programmed via a parallel port cable if your system is a DS Phat, or the card can be hotswapped with a known working one on the DS Lite.
Alternatives
Other, less popular third-party firmwares include; FWNitro, NoCash's (part of NO$GBA'S XBOO solution), CreeboMe, and CTurt's. Not all of these are cross-compatible and many few would recommend them, but are mention for further reading for the enthusiast.
Source code
The source code for FlashMe can be found here: https://gbatemp.net/download/flashme-source-code.38064/