Shark Tank is the direct US adaptation of the format behind BBC's Dragon's Den.
Shark Tank uses the same central premise: entrepreneurs present businesses to a panel of wealthy investors and seek money in exchange for equity or another negotiated arrangement. The American programme uses “sharks” instead of “dragons,” adapting the terminology while retaining the pitch-and-negotiation structure.
Both programmes ultimately belong to an international format lineage that began with the Japanese show Money Tigers. Dragon's Den is the British version, while Shark Tank became the prominent American version. They are related programmes rather than unrelated shows with merely similar themes.
The answer is sometimes confused with The Apprentice because both involve business personalities and competition. The Apprentice, however, has a different format centred on tasks and hiring rather than entrepreneurs pitching for investment.