Final answer:
Stellarium is a free, open-source software that serves as a virtual planetarium, showing the sky from any place at any time without charge.
Step-by-step explanation:
Software that you can use for an unlimited time at no charge often falls under the category of 'freeware' or 'open-source software'.
A specific example of this is Stellarium, which is a free, open-source computer application.
Stellarium is designed to show the sky at any time from any location, making it an excellent educational resource for studying astronomy.
The advantage of using software like Stellarium is that it allows for exploration and learning without the financial burden attached to some proprietary software.
The open-source nature of Stellarium also means that the code is available for anyone to review or contribute to, fostering an environment of community collaboration and improvement.