Considering helping out on the wiki to keep it updated - in particular the changed unique items need to be updated to reflect 2.6.0 changes.
Mods and base items have been updated to 2.6 values - skill progressions on some skill gem pages may need updating or some bugs need to be fixed.
Acts divide up the game into sections. Each major release adds a new act. GGG intends to have 10 acts in the game . Each act takes about 12 months to complete depending on available development resources 
- Paul Younger (October 21, 2013). "Path of Exile Interview with Grinding Gear Games CEO Chris Wilson". PC Invasion. Retrieved June 23, 2016.