Embarcadero Dev-C++ is an open source C/C++ IDE project built in Delphi. Dev-C++ has been downloaded over 67 MILLON times since 2000 and a modernization effort was sponsored by Embarcadero to bring it up to the latest version of Delphi. The original version by Bloodshed software was originally built in Delphi 6 and then probably upgraded to Delphi 7. A newer unofficial fork called Orwell Dev-C++ continued upgrading the project in Delphi 7 but the last release was in 2015. The Orwell fork of Dev-C++ uses the custom FastMM4 4.991 memory manager which came out in 2012. There is a newer version of FastMM4 4.992 which came out in 2016.

FastMM4 is a memory manager for Delphi by Pierre le Riche. It is available under both an MPL and LGPL license. Delphi actually ships with a custom version of FastMM4 and there is a discussion over on Delphi-PRAXiS about the differences between the two. FastMM4 is described as "A fast replacement memory manager for Embarcadero Delphi applications that scales well under multi-threaded usage, is not prone to memory fragmentation, and supports shared memory without the use of external .DLL files." Some of it's advantages are listed as:

Fast
Low overhead. FastMM is designed for an average of 5% and maximum of 10% overhead per block.
Supports up to 3GB of user mode address space under Windows 32-bit and 4GB under Windows 64-bit. Add the "$SetPEFlags $20" option (in curly braces) to your .dpr to enable this.
Highly aligned memory blocks. Can be configured for either 8-byte or 16-byte alignment.
Good scaling under multi-threaded applications

In 2020, developer Pierre le Riche released a complete rewrite of FastMM4 called FastMM5. As part of the Dev-C++ modernization effort we upgraded the memory manager in it from FastMM4 to FastMM5. FastMM5 is available under a GPL and commercial license. This means that it can be used with another GPL project or a commercial license can be purchased to use it with your projects. It is described as "Version 5 is a complete rewrite of FastMM. It is designed from the ground up to simultaneously keep the strengths and address the shortcomings of version 4.992".

The latest version of Embarcadero Dev-C++ (version 6) is now available with the new FastMM5 memory manager in place. A number of other enhancements are also available in the new version like an upgraded compiler (TDM GCC 9.2.0) which supports C++17 and partial C++20.

Head over and check out the full source code for the Embarcadero sponsored version of Dev-C++ with the new memory manager.