The NETLIB linear programming problems (http://www.netlib.org/lp/data/) in Standard Input Format (SIF), see https://ralna.github.io/SIFDecode/html/sif/ .
The problems are all in MPS format, which is itself a subset of SIF. The problems have been classified according to the CUTE classification system (see, Bongartz, Conn, Gould and Toint, ACM Transactions on Mathematical Software 21, 1995, pp. 123-160), and have been slightly reformatted for consistency.