One of the best players still on the open market is defensive end Dwight Freeney. The free agent has yet to find a new team, but it doesn't seem that's because there's a lack of interest in him. Several teams have been linked to Freeney, including the Detroit Lions. Ian Rapoport reports that the Lions are one of at least a few teams that have "shown interest" in Freeney.
Rapoport also reports that Freeney is expected to start taking free-agent visits next week. This means that he could finally be ready to sign with a team. At the very least, he could be getting ready to explore his options, and the Lions seem to be a potential landing spot for him.
While the Lions did just draft Ezekiel Ansah and Devin Taylor, they could still use a veteran at defensive end to provide extra depth and serve as a mentor for the younger guys. Freeney would fit the bill in that regard, and he'd take some pressure off of Ansah.
For what it's worth, the Lions were mentioned as a team that Freeney "likes" back in March, so there does seem to be some mutual interest here.