FSK441 (for meteor scatter), designed to support communication using very brief “pings” from meteor trails in the ionosphere.
FSK441 is designed for high speed meteor scatter communication using the brief "pings" of signals reflected from the ionized trails of meteors about 100 km above the earth's surface. Such pings are typically a few dB above the receiver noise and may last from ten to a few hundred milliseconds. By using these brief pings, FSK441 facilitates QSOs in the range 500 to 1400 miles (800 to 2200 km) in the amateur 2-meter and other VHF anf UHF bands.

JT44 - JT65 (for EME and extreme troposcatter), ideal for extremely weak but slowly varying signals such as those found on troposcatter and Earth-Moon-Earth (EME) paths.
JT65 is designed for communications with very weak signals of roughly constant strength. The program is able to work at levels 10-15 dB or more below the weakest intelligible CW signals, and this makes JT65 ideal for troposheric scatter and Earth-Moon-Earth (EME) communications. Smaller stations are able to complete EME QSOs much more readily with JT65 than more traditional communication modes.
Earlier program versions also supported a mode called JT44. Like JT65, JT44 was designed for EME and troposcatter.

JT6M (for meteor scatter ), is similar to FSK441 but optimized for 50 MHz.

EME Echo (for detecting and measuring your own echoes from the moon)
EME Echo mode facilitates testing station performance by measuring your echoes from the moon. It also provides tools for measuring sun noise, antenna temperature, and similar quantities relative to a chosen reference level, and for predicting the strength of your lunar echoes.

In addition to these communication modes, WSJT offers a Measure mode for testing Sun noise, etc., and an EME Calculator to help you predict the maximum strength of your own and other stations’ echoes from the moon.

System Requirements :
WSJT is designed for computers running the Microsoft Windows operating system, including the variants Windows 95, 98, 98/SE, ME, NT, 2000, and XP. Minimum hardware requirements include a 120 MHz Pentium or equivalent CPU, 32 MB of RAM, 40 MB of free disk space, a monitor with 800 x 600 or higher resolution, and a Windows compatible sound card. Recent versions of Windows may require more memory, and a faster CPU may be desirable if you run other programs while using WSJT. You will need a simple computer-to-radio interface like those required for other sound card modes such as PSK31. The DTR or RTS line of a serial communication (COM) port is used to key the push-to-talk (PTT) line of the transmitter. Connections must be made between the transceiver audio output and computer sound card input, and vice versa. Station accessories that accomplish these things are easy to build and available commercially from a number of sources.

Both FSK441 and JT44 require time synchronization between the transmitting and receiving stations. You will need a method of setting your computer clock to an accuracy of one second or better, and keeping it set. Many operators use an internet clock-setting program, while others use a GPS receiver. You may choose to set the computer clock manually to WWV or another broadcast time.