1. GNU development tools
   1. make
   2. gcc, g++, ld, ar
   3. gdb
   4. nm, objdump
   5. gprof
   6. gcov
   7. shell
      1. sed
      2. awk
      3. sed
      4. find
      5. xargs
2. Languages
   1. C
   2. C++
   3. shell
   4. Perl
   5. SQL
3. Other APIs & LIBs
   1. Pthreads
   2. Socket API
   3. Boost
   4. Zlib
   5. libXML
   6. libIPfc
   7. CGI
4. RDBM tools
   1. MySQL
   2. PostgreSQL
5. Administration
   1. OS
      1. Linux
      2. FreeBSD
      3. OpenBSD
   2. Services
      1. DNS
      2. Mail
      3. Web
      4. SQL