Comparison
Shikaku vs Inlay
Shikaku is Nikoli's rectangle-dissection puzzle. Inlay is Coronet Arcade's independent daily on that covering idea, free in any browser and with shape clues on top.
What's the same
Both tile a grid with non-overlapping rectangles, one clue per rectangle, where a number gives the area. You are done when the whole board is covered with no gaps and no overlaps.
How Inlay differs
Inlay adds shape glyphs — square, tall, wide, or free — so a clue can constrain the shape as well as the area, or the shape instead of the area. It ships a daily, an archive, and practice sizes in the browser with no login.
Verdict
Shikaku solvers will recognise Inlay immediately, with shape clues and an archive added.