Chameleon is a FREE program which allows you make selected opened windows transparent.
It allows you to customize and add the chosen opened windows which you want to make transparent with Chameleon. You can also hide the group of programs which you can select to hide automatically on pressing ctrl+win key.
It allows you to select programs windows under the hide group which you want to make transparent and hide from other. You can control over the level of transparency which you apply on the programs under Hide Group.
None of other applications which are either under Unlinked Child or those which does not come under any of the above mentioned groups will not be hidden or made transparent.
It minimize itself to system tray so it does not come in the way to other programs which are opened and remembers the settings like transparency level and group of programs selected in hide group and unlinked child group.