Here is the list of few decompilation tools / resources that you may find useful.
•IDA Pro + Hex-Rays decompiler
•Hopper disassembler (has a decompiler)
•ODA (Online Disassembler)
•Retargetable Decompiler
if the executable was compiled by gcc, you could try objdump and get the assembly
there are some tools out there that may be helpful as well:
UPS Debugger
Evan's Debugger
Assembly Language Debugger (ALD)
Insight
Data Display Debugger (ddd)
AsmBug
Dissy