Theory and Applications of Categories (or just TAC) is an online journal about category theory. In addition to new material, they also make available important classics that have been hard to find.
The website is http://www.tac.mta.ca/tac/, from which you have access to all articles in all issues. Note that
http://www.tac.mta.ca/ does not work.
Controversies: TAC is a high-quality journal with an impressive editorial board, but unfortunately it is not listed on commercial lists of prestigious journals like the “Science Citation Index” and “Current Contents”; we should fight to improve this. Unfortunately, also the citations from TAC are not yet counted on MathSciNet either, due to the unpopularity of category theory in the leadership of the AMS (see nForum discussion). Another pure category journal is Cahiers.