sdltrs is a Radio Shack TRS-80 Model I/III/4/4P emulator for Macintosh OSX, Windows, and Linux. It has been ported from Tim Mann's excellent X-Windows UNIX emulator xtrs. Instead of using the X-Window system for graphics, it uses the portable SDL library.
Why did I write another emulator? Several reasons. First, and foremost, there was no TRS-80 emulator available for Mac OS X. Since I am the author of Atari800MacX, which is based on libSDL, it made it easy for me to make a TRS80 xtrs port based on SDL, so it would run on Windows and Linux as well as Mac OS X.
Second, sdltrs provides a text menu based GUI, which is more user friendly interface than the interface xtrs provides.
Finally, sdltrs provides some other enhancements to xtrs, such as the ability to copy and paste from the host to/from the emulator, the ability to save and load the emulator state, disk indicator LED's, fullscreen display, and on the Mac, to emulate an Epson printer as well.