Final answer:
Freeware is the type of software that can be used for an unlimited time without charge, distinguishing it from shareware, trialware, and open-source software.
Step-by-step explanation:
The software that you can use for an unlimited time at no charge is Freeware. Freeware is a category of software that is available for users to download without a financial cost. It differs from shareware, which typically offers a free temporary trial period before requesting payment for continued use, and differs from trialware, which is only free for a limited trial period and then requires purchase. Open-source software, while it can also be free of charge, is categorized by its open and accessible source code, which means users are allowed to modify and share the software. Freeware, however, may not necessarily offer this level of freedom, though it is free to use as is permanently.