OFS (Olsak's Font System) is a plainTeX and LaTeX macro for managing large font collections. It has been used by Czech/Slovak users for many years. Main features include: Long names of fonts to metric file name mapping. User can specify only exact long names in your document; Support for many font encodings; Printing of catalogues of fonts, test samples of font families; Interactive macro \showfonts shows all font families you have instaled via OFS; User interface is the same for plainTeX and for LaTeX, but implementation differs: LaTeX variant of OFS uses NFSS, but plain variant implements its own font managing (may be better than NFSS); Support for math fonts including TX fonts. The author is Petr Olsak.