Thanks.
I draw layered images on paint.net, starting with the heightmap (which then gets finishing touches using gimp to work with 16 bit range).
I don't use any specific tool other than mapconv.
There's lots more map making happening on the BAR and ZK communities, though, many of which are probably compatible with older games.
BAR maps available on
springfiles
ZK maps available on
zero-k.info maps section