I miss doing the Military records. It was my favorite indexing project(s.)
Unfortunately, projects get finished and new ones appear. My favorite were census records. Keep checking. New projects are constantly appearing. If you have an Ancestry account you could check to see what their current projects are.
I found this article by googling 'indexing projects'
The ones I currently use are Citizen Archivist with the National Archives, Billion Graves and Collaborative Indexing with Geneanet. Ancestry discontinued their World Archives Project in February.