Shareware

Shareware is software distributed for evaluation, with payment requested for continued use or access to full features. It lets users try software before deciding whether to pay.

Software trial: A limited period or version of software offered so people can evaluate it before purchase. Shareware commonly uses a time-limited trial to encourage payment.
Andrew Fluegelman: An American software publisher who popularized the term freeware and developed the PC-Talk communications program. His PC-Talk distribution helped establish an early model for voluntary software payment.
Doom (video game): A 1993 first-person shooter by id Software, with its first episode distributed as shareware. Its free first episode drew players toward purchasing the complete game.
Freeware: Copyrighted software distributed for use without a purchase price, though other restrictions may apply. Freeware does not ordinarily request payment for continued use.
Nagware: Software that repeatedly displays reminders encouraging users to pay or register. Persistent payment reminders are one way shareware requests compensation.
Jim Knopf: An American programmer and publisher who distributed PC-File as user-supported software. PC-File became an influential example of software distributed for evaluation and voluntary payment.
Wolfenstein 3D: A 1992 first-person shooter by id Software, distributed in part through shareware channels. Its shareware release demonstrated how a game episode could serve as a commercial sample.
Open-source software: Software whose source code is available under licenses permitting specified use, study, modification, and redistribution. Shareware is a payment model, not a promise that source code or modification rights are available.
Freemium: A business model offering a basic product free while charging for additional features or capacity. Freemium typically keeps a usable free tier, unlike shareware that may require payment after evaluation.
Association of Shareware Professionals: A trade association founded in 1987 to support shareware authors and promote professional practices. The association organized developers around standards for shareware distribution and support.

Linked from 9 pages