Sjasm is a Z80 assembler with lots of features. It runs on PC running Windows or Linux, but the sources are included so it should be possible to compile it on other systems as well.
Sjasm 0.42 is not 100% compatible with version 0.3x. You can download SjASM 0.39g6 below, if that is a problem.
Sjasm 0.42c - Win32 executable, a debian linux executable and sources.
Sjasm 0.42b8 - Win32 executable, a debian linux executable and sources. For people that do not like the Visual Studio format.
OK, that is just the old feature list, but you get the idea. Sjasm is a Z80 assembler.
You could also download the last version of SjASM 0.3.
These bugs will not be fixed, since there is a newer version.