We still use the Windows 2000 or XP. They do not have a transparent window.
This Glass2k is so simple and small, but very strong to make any window transparent.
It is a Freeware, works on Windows 2000 and XP. The current version is Beta Version: 0.9.2.
You can download from here, or from the official site
The file size is only 56KB.
I like it. Simply is beautiful.
The official site is shown below: