Play by Post (for our game) means that the players post to our Wiki ( dragonslayers.space ) for what they want to do in the current situation. You react to what is happening, roleplay with other Travellers and various NPCs.
To this type of postings we have Fantasy Grounds up and running 24/7 for players to log in to make a skill check as appropriate or read up on something in a manual. I have all of the MgT2 materials available in FG posted and most of them shared for people to use as they need.
Then occasionally as the group wants we get together live in FG to interact quickly.
All of this is captured in chat logs that I post to the site to integrate with the timeline/calendar.
It is a good setup for asynchronous roleplay across many time zones with several players. We currently have 4 active players across 3 time zones in North America. Our UK player dropped out but they were able to comfortably play on their schedule.