The base64 source code that I released in 2001 (http://base64.sourceforge.net/b64.c) has found very wide application and is used in remarkably diverse software. Below are some examples.
In the preamble to the code, I say that 'Generally' "This program is designed to survive:" I would say that it has done admirably in that regard. However, it is not form, nor even function that I think is responsible for its travel. It is a combination of there being few reasonable alternatives, this *being* a reasonable alternative AND the function itself is ubiquitous. Nearly every kind of non-trivial software eventually deals with mail (there is an old programmer's joke about this) and mail means attachments and attachments mean MIME and MIME means base64 encoding. Chances are; this is not even that well traveled as such. It may just be the 'luck of the draw' that there are so many requirements for this that mine was adopted by chance. I like to think the fact that there were (and are), no known bugs after seven years of use has something to do with it. I also fancy it was well written. I like to think it pleased other programmers, as it was intended to do. YMMV. Note that at least *some* of these programmers had a clue.
Editing application The World Wide Web consortium's HTML editor. This is the body responsible for setting the standards for web pages on the Internet http://dev.w3.org/cvsweb/Amaya/thotlib/dialogue/base64.cpp?rev=1.4&content-type=text/x-cvsweb-markup
Secure Operating System Stanford University -- Histar Secure Operating System. http://www.scs.stanford.edu/histar/jos64/lib/base64.c
Gammu utility and library for mobile phones http://cihar.com/gammu/docs/coding_8c.html
WebClaire Claire language kernel. http://www.claire-language.com/cgi-bin/trac.cgi/browser/trunk/xl/kernel/clSystem.cpp?rev=1667
Asterisk Voice over IP Appliance (http://www.digium.com) http://svn.digium.com/view/asterisk/team/group/xcon_bfcp/apps/xcon_bfcp/bfcp_base64.c?view=markup
ziproxy -- HTTP proxy server http://ziproxy.sourceforge.net/
Epona Internet Relay Chat (IRC) libraries http://bugs.epona.org/cgi-bin/trac.cgi/browser/libraries/misc/base64.cc
Word Document to PDF file converter http://doc2pdf.sourceforge.net/
Colorado State University Network Security -- Reflected DNS daemon https://www.netsec.colostate.edu/dnsmonitor/files/README
OpenQM post-relational database http://www.openqm.org/downloads/readme.txt
HDTV Set Top Box (Digital Television) http://www.pacemicro.com/media/americas/PDF/manuals/tdc575d_manual.pdf
WinRSA -- Public key encryption for Windows http://users.cs.cf.ac.uk/Antonia.J.Jones/Freeware/Encryption/licence.txt
Partman-Crypto (use in Debian Installer -- http://en.wikipedia.org/wiki/Debian-Installer) Note that the b64.c code is used in a number of places in most major Linux Distributions. http://packages.debian.org/changelogs/pool/main/p/partman-crypto/partman-crypto_24/copyright
SMTP Stress Testing Tool http://xstress.sourceforge.net/
Philips Flat Panel Television Sets (i.e. http://www.p4c.philips.com/files/4/47pfl5432d_37/47pfl5432d_37_pss_aen.pdf) http://www.p4c.philips.com/files/4/47pfl5432d_37/47pfl5432d_37_osr_aen.txt
Technical University of Denmark, Key Management in Cryptographic Access Control (Thesis) http://www2.imm.dtu.dk/pubdb/views/edoc_download.php/4447/pdf/imm4447.pdf
eMail -- Command line SMTP email utility. http://svn.cleancode.org/svn/email/src/mimeutils.c
Recommended by IBM for use with IBM Communications Server http://www.redbooks.ibm.com/redbooks/pdfs/sg247340.pdf
Spam Decoding Tools http://www.futuresoft.dk/mirrors/spamlinks.net/tools-deobfuscate.htm
Research Software http://portal.acm.org/citation.cfm?id=1151835&jmp=cit&coll=ACM&dl=ACM&CFID=15151515&CFTOKEN=6184618
Voice over IP telephony (software telephone) openwengo http://dev.openwengo.com/trac/openwengo/trac.cgi/browser/wifo/trunk/eXosip/src/base64.c