On my 4MB STfm running MiNT with monochrome monitor, I used ImageCopy and mGIF. Last one was great for viewing pictures I'd rendered with Pov-Ray (overnight), as it had this mode "flicker" mode which showed color images as grayscale on the Atari monochrome monitor.
MGIF convolution matrices were also nice if one wanted to do some image manipulation tricks similar to Linux Gimp's image filters.
For BBS mails I used Kivi QWK reader, but that's not very relevant anymore.
For text editing, Everest...