MiNT (MiNT is Now TOS) is a free software alternative operating system kernel for the Atari ST and its successors. Together with the free system components fVDI (device drivers), XaAES (GUI widgets), and TeraDesk (a file manager), MiNT provides a free TOS compatible replacement OS that is capable of multitasking.
MiNT was originally released by Eric Smith as "MiNT is Not TOS" (a play on "GNU's Not Unix"). Atari adopted MiNT as an official alternative kernel with the release of the Atari Falcon, slightly altering the MiNT acronym into "MiNT is Now TOS". Atari bundled MiNT with AES 4.0 (a multitasking version of GEM) under the name MultiTOS. After Atari left the computer market, MiNT development has been continued by a core of volunteers. Nowadays the official name has been changed to "FreeMiNT" upon request by Eric Smith. The reason for this was to distinguish it from the versions that were released by Atari.
There are several distributions, most notably the RPM-based SpareMiNT as well as the Debian GNU/MiNT porting effort.
Read more about MiNT: AES For MiNT