The TLA+ Video Course by Leslie Lamport
TLA+ is fantastic. Knowing it is like having superpowers. While others are mortally afraid of concurrency, you just spec your system & go. It also gives a huge decrease in cognitive load when you're implementing your system against a TLA+ spec. The hard stuff is already done. You can just glance at the spec to see what preconditions must be checked before an action is performed. No pausing halfway through writing a function as you suddenly think of an obscure sequence of events that breaks your code.