Facebook is doing a lot of ML work on automated tracing from aerial imagery, which has great potential for mapping terra incognita in OSM. There are several bumps to be ironed out with the community but they're engaging well.

Bing has given OSM tracing rights over its aerial imagery for several years now - it's hard to overestimate how significant that is.

Apple (as you'd expect) has been much more private about its OSM work, but it has numerous people working on it and has been surfacing OSM data in Apple Maps in several parts of the world.

Facebook and Bing were both Gold sponsors of the most recent State of the Map US: https://2017.stateofthemap.us though in fairness Google was a bronze sponsor

Bing was a gold sponsor of the most recent State of the Map (global conference) in Japan, Facebook silver: http://2017.stateofthemap.org

Bing has for years allowed the use of their sat images for OSM tracing.

Bing has allowed OSMers to trace from their aerial imagery for years. Having proper aerial imagery is like night and day for mapping.

It used to be Yahoo aerial in the early days.