Every time tup comes up, there's a question I have that nobody seems to know the answer to: how does tup know what changed? Make does this by starting from what it needs to build (which it knows) and traversing the dependencies. Does tup have some sort of daemon that monitors the file system? What if the file system isn't local (NFS, say)?
You can have a daemon (tup monitor), but it is not required; in the second case tup will compare last-mod times of files with those from the last run (stored in the .tup dir).
