A toolchain is the set of tools to go from source to executable (compile => assemble => librarian => linker)
Comments are welcomed! Also could list the editor/IDE tool you use…
I use quite exclusively Eclipse for all development tasks, and SciTE or nano for occasional quick editing.
I fit in two categories though… I still use MPASM sometimes, and adding features to MB-SID is done in MPASM, but it’s easier to develop new code with sdcc.
Same as Wilba…
Windows + ( (MPASM) || (GPUtils) || (GPUtils + SDCC + ( (CodeBlocks) || (NotePad++) ) ) + Perl + Stuff
Short answer: It depends 
ditto, Started with wintel/mpasm (the platform I make most of my funds with… thank you Bill Gates for selling me an MCP,MCSE,etc…to support your MS CRAP!)… tried MacOS, (my platform of pref), Linux on pc, Spark, and Mac…
final platform, old wintel laptop / win2k.