A work in progress is a project that is not yet finished or polished. One might say this about a work assignment, a home renovation, or about one’s relationship with another person. No hyphens are necessary. The plural form is works in progress. Be careful when distinguishing between a group’s work in progress and their works in progress, the former is one project belonging to multiple people and the latter speaks of multiple projects.
Sometimes this is used as an adjective and then should be hyphenated as a compound modifier; however, this construction is slightly awkward. Shortening it to in-progress carries the same meaning as is much easier for the reader.
This shortening is used as a phrase as well, modifying anything the user wishes to deem as unfinished (e.g., team in progress, dinner in progress, etc.)
A work in process is synonym for some with work in progress. However, work in progress is much more common. For some users in accounting and manufacturing, there is a distinction between inventory and assets, but outside of those fields the difference is negligible.
The confusion between the two phrases comes in part from the acronym WIP, which logically could mean work in progress or process.
Three years of renovation and the children’s park is still a work in progress. [The New Indian Express]
Tetzlaff has recorded Bach’s unaccompanied violin works twice already, but his performances here still seemed like works in progress, in the best sense. [The Guardian]
But for many photographers who are versed in the ways of film, the transition is a work in process. [Tanzania Daily News]
Cavaradossi’s in-progress painting of Mary Magdalene becomes a vast, heavy-framed, raked floor (huh?) where most of the action transpires. [The Dallas Morning News]