I’ve been keeping a personal Google Sites page where I log every manga I finish and rate arcs. It started as a way to remember details for discussions with my friends who are deep into seinen stuff like Berserk and Vinland Saga. The site is super simple—just color-coded tables and my notes on pacing.
One honest downside: it took me a while to get the layout right because Google Sites isn’t built for complex databases. But for a free space to share my watchlist with my buddies, it works. Here’s my profile: sites.google profile. I update it every time I finish a series, usually after marathoning a new shonen like Jujutsu Kaisen.