The tau mass can be measured using the pseudomass method in 3-prong tau decays and using Z to tautau events where both taus decay to hadrons and the tau direction can be calculated. The first method is expected to be more precise in Z decays . The expected statistical precision is of order 1 MeV/c^2. 

References, see : 
P. Privitera: "A Measurement of the tau mass",  DELPHI Note 93-58 PHYS 286  
 

By studying the vector and non-vector spectral functions in hadronic tau decays one can obtain a measurement of alpha_s on the tau mass scale.  

References, see for example:  
Recent Aleph publication: European Physical Journal C4 (1998) 409 and references therein. 
 

By studying the spectral functions in strange tau decays it is possible to measure the strange quark mass at the tau mass scale. This should be particularly interesting for DELPHI with the RICH. 
  
References, see for example: 
Recent Aleph publication: CERN-EP-99-026  
 

With optimised CP-sensitive variables constructed from correlations between different taus in a Z to tautau event it is possible to put a limit on the weak dipole moment of the tau. 

References, see for example:  
M.C. Chen et al, DELPHI submission to Warsaw conference. Delphi note  96-111 Warsaw CONF 38.
Recent Opal publication: Zeit. fur Physik C74 (1997) 403 - 412 and references therein. 
 

Through the study of radiative Z to tautau events and the production rate of tautau events in two-photon collisions it is possible to set upper limits on the tau anomalous magnetic and electric dipole moments. 

References, see for example:  
Recent L3 publication:  Phys. Lett. B 434 (1998) 169-179 and references therein.  
 

The fully polarised taus produced in W decays give higher sensitivity to the polarisation related michel parameters  xi and xi-delta. Its should be possible to reach a similar level of precision with the WW data set produced at LEP 2 as was acheived at LEP-1 with the full tau pair sample. 

References: none