A few improvements could be made to DASSL:

• replace LINPACK routines with their LAPACK counterparts
• link against an optimized BLAS library

It would also be of interest to provide a PDECHB callback compatible with the newer DASPK solver. DASPK can be found on Netlib: https://netlib.org/ode/. The method is described in

Brown, P. N., Hindmarsh, A. C., & Petzold, L. R. (1994). Using Krylov methods in the solution of large-scale differential-algebraic systems. SIAM Journal on Scientific Computing, 15(6), 1467-1488. https://doi.org/10.1137/0915088

A few more DAE solvers can be found in the Netlib folder (e.g. daesolve). Other notable ones include:

• SolveDAE (related to dgelda on Netlib)
• Sundials IDA (derived from DASPK)