What are the differences between HPRD and BIOGRID databases?
Short Answer

In a nutshell, there are two major differences:


Species range: BioGRID integrates multiple species' protein-protein interaction (PPI) data, whereas HPRD focuses mainly on Human data.
Functionality: HPRD has some GUI tools that can interact directly with it's database (e.g. BLAST - for searching proteins and their binding partners via sequence alignment) whereas BioGRID is mostly just a database.




Long Answer

In bold are the unique features of each database.

About HPRD:


  The Human Protein Reference Database represents a
  centralized platform to visually depict and integrate information
  pertaining to domain architecture, post-translational modifications,
  interaction networks and disease association for each protein in the
  human proteome. All the information in HPRD has been manually
  extracted from the literature by expert biologists who read, interpret
  and analyze the published data. HPRD has been created using an object
  oriented database in Zope, an open source web application server, that
  provides versatility in query functions and allows data to be
  displayed dynamically.
  
  FAQ HPRD: Why did you decide to develop yet another database instead of integrating other existing databases?"
  We believe that biological databases are still in their early stages
  and no protein database can be considered as an established standard.
  We feel that a variety of databases trying to solve problems in
  diverse ways provide the biologists the possibility of choosing their
  favorite. Our approach is radically different from existing databases
  and we want to offer biologists the possibility of choosing instead of
  imposing one database by default. Besides, most of the databases are
  automated and ours is manually curated to avoid errors. We are also
  trying to provide information that few other databases provide.


About Biogrid: 


  The Biological General Repository for Interaction Datasets (BioGRID)
  is a public database that archives and disseminates genetic and
  protein interaction data from model organisms and humans
  (thebiogrid.org). BioGRID currently holds over 720,000 interactions
  curated from both high-throughput datasets and individual focused
  studies, as derived from over 41,000 publications in the primary
  literature. Complete coverage of the entire literature is maintained
  for budding yeast (S. cerevisiae), fission yeast (S. pombe) and thale
  cress (A. thaliana), and efforts to expand curation across multiple
  metazoan species are underway. Current curation drives are focused on
  particular areas of biology to enable insights into conserved networks
  and pathways that are relevant to human health. The BioGRID 3.2 web
  interface contains new search and display features that enable rapid
  queries across multiple data types and sources. BioGRID provides
  interaction data to several model organism databases, resources such
  as Entrez-Gene, SGD, TAIR, FlyBase and other interaction
  meta-databases. The entire BioGRID 3.2 data collection may be
  downloaded in multiple file formats, including IMEx compatible PSI MI
  XML. For developers, BioGRID interactions are also available via a
  REST based Web Service and Cytoscape plugin. All BioGRID documentation
  is available online in the BioGRID Wiki.