MimbleWimble is novel in that it offers privacy and efficiency enhancements hand in hand through a unique combination of the protocol’s version of confidential transactions, CoinJoin, and cut-through within and among blocks to make it possible for more devices to partake in securing network.
Grin and Beam are both implementations of MimbleWimble, but their similarities stop there. Ignotus Peverell (Grin’s creator) points out that “a common misconception is that MimbleWimble describes a full cryptocurrency solution and therefore tend to lump Beam and [Grin] in the same basket.”
While both projects seek to offer their users privacy and efficiency improvements, they differ in most technical, structural, and organizational elements. The difference that has ignited the most discussion is the sustainability of Grin’s donation and volunteer-driven/cypherpunk approach (similar to Bitcoin and Monero) versus Beam’s VC-backed startup approach with it’s founder’s reward and paid employees (similar to Zcash). Time will tell which approach is superior. Until then, it will be interesting to see how these projects play off of and learn from one another.