A bit of an assumption yes, here's my reasoning though. Traceur and Typescript (and perhaps Flow and AtScript) are similar efforts made by different players that require transpilation and are potential visions for a direction javascript could go in. This combined with the author's quote "All of the other players..." made me think that's the family of solutions they were referring to.
NaCl and Dart are both by a single player and there's nothing else like them that I know about but Mozilla's asm.js, which the author is praising here, so they didn't seem like likely candidates.
NaCl and Dart are both by a single player and there's nothing else like them that I know about but Mozilla's asm.js, which the author is praising here, so they didn't seem like likely candidates.