Here’s a list of some of the BASIC expansions, compilers and interpreters available for Sinclair computers.

Expansions:

• Beta BASIC (Spectrum): +60 new commands – Graphic commands – Structured programming – Programmers toolkit (Link)
• YS Mega BASIC (Spectrum): +35 new commands -Windows – Sprites – Structured programming (Link)

Compilers and Interpreters:

• HiSoft BASIC (Spectrum): BASIC to machine code compiler – Compiler directives. (Link)
• MCoder II (Spectrum): BASIC to machine code compiler – Only integers. (Link)
• MCoder II (ZX-81): BASIC to machine code compiler – Only integers – Limited string support. (Link)
• Wye Compiler (Spectrum): BASIC to machine code compiler – Extended commands (Link)
• Boriel’s ZX BASIC compiler (Spectrum): BASIC to machine code crosscompiler written in Python (Link) (*)

(*) Boriel’s ZX BASIC uses it’s own BASIC dialect, but according to the rules for crossdevelopment tools the BASIC listing should be runnable natively. This means a program written in ZX BASIC should be compliant with Sinclair BASIC commands and sintax (lines must be numbered and no use of ZX BASIC own commands and datatypes)

Note: For those expansions, interpreters or compilers that allow to include inline assembly on the BASIC program,  such feature should not be used as it collides with the competition’s rules.