UAE - Classic AmigaOS emulation on x86 systems

UAE started life as a rather nasty and slow little emulator that could play a few limited classic Amiga games. At that point, it stood for "Unusable Amiga Emulator" due to it's hideously slow speed and many many incompatibility issues. Howveer, as it progressed and became faster and far more usable, it's name changed to the "Un*x Amiga Emulator". Then it spread to multiple platforms and for a long time was known as the "Ubiquitous Amiga Emulator". However now, even that name is becoming deprecated and it is quite simply, UAE.
UAE is, and always has been, targetted at emulating an Amiga completely as opposed to other systems such as Amithlon which sacrifice a little bit of completeness for a lot of speed.
UAE is avaialable for a very wide variety of platforms including both MSWindows and Linux and is a continual work in progress.

Because UAE emulates an Amiga, it of course requires Amiga ROMs and software. As these are copyrighted products, they cannot be legally distributed despite the unfortunate number of people who do so.
This does NOT mean that UAE is an illegal product however - there are plenty of ways to use it legally. If you own Amiga ROMs, you can take an image of them using a piece of software and use this image legally with UAE. Alternatively, you can purchase "Amiga Forever" from Cloanto which includes licensed ROMs and a bunch of other goodies.

Setting up a full Amiga system under UAE can be quite daunting for people unfamiliar with Amiga however - after all, it's not the real thing and has it's own little quirks and problems. For such people, there is Amiga in a Box which is a freely downloadable "snapshot" of a fully set up and working system.

Many people argue that UAE is good for nothing but playing games. While I'll agree it's about the best Amiga games emulator out there, it is still an excellent alternative to Amithlon, for while it doesn't run as "natively" as Amithlon does, and lacks a certain "feel" and some of the speed, it's latest incarnations are pretty spectacular on a decent system AND can do things such as sharing the host OS TCP/IP stack (very handy if you want to browse the web with Internet Explorer but chat on IRC with AmIRC for example)