Hanabi entails a great depth of strategy, yet has relatively few rules (and game pieces). As such, it's relatively simple to conceive and implement rules variations -- variants -- that preserve the spirit of Hanabi. Physical game releases include descriptions of some variants and the extra tools needed to play them -- for example, the original releases included a sixth and rainbow-coloured suit along with the description of how to play three variants using that suit. hanab-live has a large number of fully enumerated variants (incluing all those described in physical releases; the three aforementioned original variants are called 6 Suits, Black (6 Suits), and Rainbow (6 Suits) there).
The concept of the "spirit of the game" is a highly subjective one. The rest of this section is the opinion of one author.
It's not particularly important to precisely define the spirit of Hanabi. Based on my own thoughts, and evidence from what rule variations have been discussed and implemented, I would summarize the spirit as follows:
This interpretation leaves a huge space for rules varations. With that laid out, let's discuss the game parameters that can and have been varied.
The types of clues available to give in a game are often considered along with the suits as a single unit of variation, related by the clue map. Furthermore, several parameters relating to clues can be varied:
One example from hanab-live where all of these are varied is the "Clue Starved" family of variants. In these variants[1], the token cost to give a clue is increased (with respect to the base game) to two, while the maximum and starting clue count are increased to sixteen.
Variants implemented on hanab-live can be found here.
The clue token values are presented in the hanab-live interface as half of how they're described here, such that the two descriptions are equivalent. I.e. on hanab-live, in Clue Starved variants, the clue token benefit of discarding and successfully playing a 5 are presented as being one half, while the maximum and starting count and cost for clue action remain as being one. ↩︎