From many sources, as seen in the list below. While deploying reference stations (so called NTRIP Servers) can be very costly, and NTRIP Casters other than SNIP often cost thousands, as a rule NTRIP Clients are typically provided for free and can be readily downloaded over the web.
Also, be sure to first ask you dealer or device vendor. Many, if not most, GNSS vendors can provide or recommend an NTRIP Client to use.
If Client, Caster, and Sever are still strange terms, read about them here.
Here is a short list to start your search. Note that many of these products use similar names.
NTRIP Client a very simple easy to use and free PC based product offered by Lefebure Design, LLC
see the site at: http://lefebure.com/software/ntripclient/
Lefebure NTRIP Client for Android a free android product offered by Lefebure Design, LLC
see the Google Apps store site here and you will notice there are several derivative apps as well.
RTKLIB the open source RTK tool (several tools contain clients) developed by Tomoji Takasu
see the site at: http://rtklib.com/
RTK Explorer Various useful improvements to the the RTKLIB tool above (added by Tim Everett) and now often preferred over RTKLIB as new updates are being added.
see the site at: http://rtkexplorer.com/
BKG Ntrip Client (BNC) the free product offered by BKG, this is a comprehensive tool with many features. See the site at: http://igs.bkg.bund.de/ntrip/download This tool is the first entry in the list; just pick your preferred OS.
NtripClient the free product offered by Dirk Stoecker Alberding GmbH
see the site at: https://www.dstoecker.eu/
GnssSurfer the free PC product offered by Juergen Siebert, SAPOS
see the site at: http://188.8.131.52/Download/GnssSurferV1.10.zip
SXBlue RTN is a free client for WinCE offered by Geneq Inc.
see the site at: http://www.sxbluegps.com/download/
GNSS Internet Radio, is an older (free) Window GUI product offered by BKG it is sort of a grandfather in all this (before the term NTRIP was coined) and no longer updated these days, but the source code makes a good starting point and we include it for completeness. Here is a read me page that describes it. The tool is no longer distributed by BKG (as other tools have overcome it) but you can find some mirror links. And here is a great history lesson from The American Surveyor that mentions it as well.
NOTE: If you know of a client you feel should be listed here, please drop us a note.
In the above and the BNC list you can find client software for all the major operating systems, and a number of these products / firms also provide their code as open source.
Need to write your own client for an embedded project? The above products cover C, C++, VB, Java, PHP and a few other languages. If you have prior experience in developing sockets and/or serial port, you will find the process fairly easy. Here is the BKG FTP site with a huge pile of useful client source code to browse and consider.
Most of the above products presume that there is a TCP/IP connection which can be used to connect to the NTRIP Caster, and then a local serial port or Bluetooth which connects to your rover GNSS.
There are many other products that handle the wireless “last mile” to make a wireless connection to your rover. Historically that last mile link has been a separate industry within GNSS where point to point or broadcast radio devices have been used. Even today, the typical RTK survey crew often comes to the site with sets of private radios to overcome this issue.
Now that cellular coverage is available in much of the world, this is less of an issue. However, some applications still require a local radio link. Many people use WiFi or WiMax or this, others use 900MHz, 2.4GHz, or 5.8GHz radio links in the unlicensed ISM bands. The precise regulations and rules vary depending on what part of the world you live in. The rapid growth in RTK applications for aerial drone use has changed the landscape in this respect. Short range radio transmitter circuit boards can be obtained by hobbyists for tens of dollars, allowing them to connect over small regions.
At this time, SNIP provides direct TCP/IP connectivity, but it does not link directly to or operate radios, and often this is not needed. We expect to add direct push support for several of the more popular radio links as a future product feature.
Also see this knowledge base article for more NTRIP Client sources.