JFFS2
Journalling Flash File System version 2 or JFFS2 is a log-structured file system for use with flash memory devices. It is the successor to JFFS. JFFS2 has been included in the Linux kernel since the 2.4.10 (2001-09-23) release. JFFS2 is also available for a few bootloaders, like Das U-Boot, Open Firmware, the eCos RTOS and the RedBoot. Most prominently JFFS2 is used in OpenWrt.
Read more about Jffs2.