sinclair
The extremely popular and successful computers from England-based legendary Sinclair Research were shipped with BASICs developed by Nine Tiles Networks Ltd, also an English company. These BASICs were pretty similar among its own evolutions and also to Microsoft BASIC-80-based interpreters which were so common at the time. It was not hard to port programs written for the Sinclair Spectrum to a MSX machine, for example.
Most keywords from its first version, the 4KB BASIC for the tiny ZX80, were ported to its later versions (though with different capabilities sometimes), so the ZX80 version is the Sinclair baseline referred to by this site's Keywords section. It was an incomplete implementation of ANSI Minimal BASIC with integer-only arithmetic in order to fit into 4KB of ROM.
Several extensions were published by third-party companies and by Sinclair itself.