Xbase is a TCP/UDP socket library for creating multi-client and multi-server programs such as proxies, chat, file transfer, HTTP, SMTP, POP3, FTP, and DNS. It is available for 32 and 64-bit Windows 10 and is royalty-free.

I particularly liked how easy it was to create chat servers and clients, as well as client/server file transfer programs. The library also allows you to create client programs that can communicate with a variety of TCP servers, including POP3, IMAP, HTTP, FTP, SMTP, and DNS. Additionally, you can connect to a device by sending commands to its IP address and create SMTP proxy programs that extract a copy of all recipient addresses, POP3 proxy programs that filter incoming email for spam, and HTTP proxies used to filter content.
The Xbase TCP and UDP socket library client/server component allows for the sending and receiving of data buffers or entire files and servers can handle multiple connections concurrently. You can run multiple servers and clients simultaneously, and specify the maximum number of connections that the server will accept. The library supports both TCP and UDP protocols and includes multiple Xbase example programs.
One of the best things about the Xbase TCP and UDP socket library client/server component is that it does not depend on support libraries and only calls core Windows API functions. Royalty-free distribution with your compiled application is included, and C source code is available. Additionally, the library comes with one year of free technical support and updates and a fully functional evaluation version is available. Finally, it works with all 32-bit versions of Xbase and 32-bit and 64-bit Windows through Windows 10. I highly recommend this library to anyone looking to create robust and secure client/server applications.
Version 7.1: Fixed problem with cscFileCRC() and cscCryptoPutFileExt(). Added cscTestDotted(). Fixed problem in cscRelease(). Increased MAX_DATA_SIZE from 30000 to 50000 bytes. Added CSC_SET_SOCK_REUSE [to cscSetInteger()].