An important distinction is while fasting for Ramadan, you can't ingest anything at all, including water. Unlike intermittent fasting where practitioners might still have 0 calorie coffee to stay stimulated, and water to stay hydrated.
I also think some others, among them Christians, fast completely.
Personally I am Christian but when I fast, the vast majority of the times it has been because I was bored or needed to focus, and I didn't punish myself by breaking fast once a day but just went without food a day or two or three until I became bored of that too or family demanded I ate.