Old Church Slavonic or Church Slavonic is a literary language which developed from the language used by St Cyril and St Methodius, 9th century missionaries from Byzantium, to translate the bible and other religious works. Cyril and Methodius based their translations on a Slavonic dialect of the Thessalonika area and invented a new alphabet, Glagolitic, in order to write them.
Sometime during the 10th century AD a new alphabet appeared which was known as Cyrillic and named after St Cyril, though it was possibly invented by St Kliment of Ohrid. The Cyrillic alphabet was used to write the Old Church Slavonic language and was later adapated to write many other languages.
Old Church Slavonic was used as the liturgical language of the Russian Orthodox church between the 9th and 12th centuries. A more modern form of the language, known as Church Slavonic, appeared during the 14th century and is still used in the Russian Orthodox church.
Luke 2: 1-4
Source: http://www.utexas.edu/cola/depts/lrc/eieol/ocsol-7-X.html
Longer sample text (Tower of Babel)
Free Old Church Slavonic fonts
http://www.wazu.jp/gallery/Fonts_CyrOCS.html
http://babel.uoregon.edu/yamada/fonts/ocslavonic.html
http://clover.slavic.pitt.edu/~aatseel/fonts/wincyrillic.html
http://www.davidzbiral.webzdarma.cz/cyrillicof.htm
Online Church Slavonic lessons
http://justin.zamora.com/slavonic/
http://www.orthodoxepubsoc.org/etutorindex.htm
http://www.utexas.edu/cola/depts/lrc/eieol/ocsol-TC.html
Online Church Slavonic keyboard
http://www.churchslavonic.org
Online Church Slavonic Institute
http://public.srce.hr/staroslavenski-institut/en/home.html
Corpus Cyrillo-Methodianum Helsingiense (An Electronic Corpus of Old Church Slavonic Texts): http://www.slav.helsinki.fi/ccmh/
ALPHABETUM - a Unicode font specifically designed for ancient scripts, including classical & medieval Latin, ancient Greek, Etruscan, Oscan, Umbrian, Faliscan, Messapic, Picene, Iberian, Celtiberian, Gothic, Runic, Old & Middle English, Hebrew, Sanskrit, Old Nordic, Ogham, Kharosthi, Glagolitic, Old Cyrillic, Phoenician, Avestan, Ugaritic, Linear B, Anatolian scripts, Coptic, Cypriot, Brahmi, Old Persian cuneiform: http://guindo.pntic.mec.es/~jmag0042/alphabet.html
Belarusian, Bosnian, Bulgarian, Croatian, Czech, Kashubian, Macedonian, Old Church Slavonic, Polish, Russian, Rusyn, Serbian, Silesian, Slovak, Slovenian, Sorbian, Ukrainian
Armenian, Avestan, Bassa (Vah), Beitha Kukju, Carian, Carpathian Basin Rovas, Coptic, Cyrillic, Dalecarlian runes, Elbsan, Etruscan, Fraser, Georgian (Asomtavruli & Nuskha-khucuri), Georgian (Mkhedruli), Glagolitic, Gothic, Greek, Hungarian Runes, Irish, Khazarian Rovas, Korean, Latin, Lycian, Lydian, Manchu, Meroïtic, Mongolian, N'Ko, Ogham, Old Church Slavonic, Oirat Clear Script, Old Italic, Old Permic, Orkhon, Phrygian, Pollard Miao, Runic, Santali, Somali, Sutton SignWriting, Tai Lue, Thaana, Todhri, Uyghur