Rather than pointlessly regurgitate all the usual modelling and simulation links, perhaps I should just direct you to the Population Approach Group in Europe (PAGE) homepage for those.
Here are a few more which are more relevant from a software development point of view:
Perl-speaks-NONMEM (PsN) is a collection of Perl modules and programs aiding in the development of non-linear mixed effect models using NONMEM. The functionality ranges from solutions to simpler tasks such as parameter estimate extraction from output files, data file subsetting and resampling, to advanced computer-intensive statistical methods. PsN includes stand-alone tools for the end-user as well as development libraries for method developers.
Perl is a stable, cross platform programming language. It is used for mission critical projects in the public and private sectors. Perl is Open Source software, licensed under its Artistic License, or the GNU General Public License (GPL).
Xpose is an R library designed to carry out statistical and graphical analysis of NONMEM output.
R is a free software environment for statistical computing and graphics. It compiles and runs on a wide variety of UNIX platforms, Windows and MacOS. One day soon you will need it to get the most out of Census.
Lazarus is a cross-platform integrated development environment (IDE) that lets you create visual (GUI) and non-visual Object Pascal programs, and uses the Free Pascal compiler to generate your executable. Its aim is write once, compile anywhere: you should be able to just recompile your program source code with Lazarus running on another operating system (or a cross compiler) and get a program that runs on that operating system.
Free Pascal (aka FPK Pascal) is a 32 and 64 bit professional Pascal compiler. It can target multiple processor architectures: Intel x86, AMD64/x86-64, PowerPC, PowerPC64, SPARC, and ARM. Supported operating systems include Linux, FreeBSD, Haiku, Mac OS X/iOS/Darwin, DOS, Win32, Win64, WinCE, OS/2, MorphOS, Nintendo GBA, Nintendo DS, and Nintendo Wii. Additionally, JVM, MIPS (big and little endian variants) and Motorola 68k architecture targets are available in the development versions.
SQLite3 is version 3 of a software library that implements a self-contained, serverless, zero-configuration, transactional SQL database engine. SQLite is the most widely deployed SQL database engine in the world. The source code for SQLite is in the public domain.