CSplain is a small extension of basic Plain TeX macros from which the formats csplain and pdfcsplain can be generated. It supports: hyphenation of words for 50+ languages, simple and powerful font loading system (various sizes of fonts), TeX, pdfTeX, XeTeX and LuaTeX engines, math fonts simply loaded with full amstex-like features, three internal encodings (IL2 for Czech/Slovak languages, T1 for many languages with latin alphabet and Unicode in new TeX engines), natural UTF-8 input in pdfTeX using encTeX without any active characters, Czech and Slovak special typesetting features. An important part of the package is OPmac, which implements most of LaTeX's features (sectioning, font selection, color, hyper reference and URLs, bibliography, index, table of contents, tables, etc.) by Plain TeX macros. The OPmac macros can generate a bibliography without any external program.