I'm not familiar with the program, but attempting to research it, I couldn't find a single word explaining the difference, and the terms are used interchangeably. Web sites (including the official project sites), have a title containing one term and content containing the other, with no explanation. My guess from the context is that aria2 is the project and aria2c is the executable.
The proposed wiki edits that raised the question were an attempt to copy the aria2 wiki and excerpt content to the aria2c tag. This appears to be a case where the separate tags are not serving a useful purpose.
- Whatever the difference is between the two should be made clear in the tag wikis, and the excerpts should provide guidance on when to use each.
- If the difference is unimportant, the tags should be synonomized, or one of them eliminated and the two terms be covered in the remaining wiki and excerpt.
If I was familiar with the program, I would just fix it (and I'll be happy to do that if somebody can explain the difference). So I'm raising the question so people familiar with it can either clarify or do the honors.