I have been maintaining ports of Pico]OS for arm7tdmi, Arm Cortex-M, Texas Instruments MSP430 and unix. Arm7tdmi is mainly for Philips/NXP LPC2xxx series, although there are other, untested cpu families in that port. These ports are included in recent official Pico]OS downloads.
As I was writing Cortex-M port I started thinking that it would be possible to implement arm7tdmi port using a little bit similar design. This resulted in a little bit experimental port for lpc2xxx CPU family, which has less plain assember than original arm7tdmi port. It has also simpler linker scripts for gcc as most of common stuff has been gathered into shared include file.
And don’t think that Pico]OS is dead because it’s core is not actively developed – it is not. It has just matured.
Source code is available at Github.