TclCurl

TclCurl is a library that provides a binding to libcurl for the Tcl programming language. Some of its key features are as follows:

Misc:
- Full URL syntax
- Custom maximum download time
- Custom least download speed acceptable
- Multiple URLs
- Guesses protocol from host name unless specified
- Uses .netrc
- Progress bar/time specs while downloading
- "Standard" proxy environment variables support
- Config file support
- Redirectable stderr
- Use selected network interface for outgoing traffic
- IPv6 support
- Persistent connections

HTTP:
- HTTP/1.1 compliant
- GET
- PUT
- HEAD
- POST
- Multipart POST
- Authentication
- Resume (both GET and PUT)
- Follow redirects
- Maximum amount of redirects to follow
- Custom HTTP request
- Cookie get/send fully parsed
- Understands the netscape cookie file format
- Custom headers (that can replace/remove internally generated headers)
- Custom user-agent string
- Custom referer string
- Range
- Proxy authentication
- Time conditions
- Via http-proxy
- Retrieve file modification date

HTTPS (*1):
- (All the HTTP features)
- Using certificates
- Verify server certificate
- Via http-proxy
- OpenSSL engines

FTP:
- Download
- Authentication
- Kerberos security
- PORT or PASV
- Single file size information (compare to HTTP HEAD)
- 'type=' URL support
- Dir listing
- Dir listing names-only
- Upload
- Upload append
- Upload via http-proxy as HTTP PUT
- Download resume
- Upload resume
- Custom ftp commands (before and/or after the transfer)
- Simple "range" support
- All operations can be tunneled through a http-proxy
- Customizable to retrieve file modification date

FTPS(*1:
- TELNET
- Connection negotiation
- Custom telnet options
- Stdin/stdout I/O

LDAP (*2):
- Full LDAP URL support

DICT:
- Extended DICT URL support

GOPHER:
- GET
- Via http-proxy

FILE:
- URL support.

Overall, TclCurl offers a wide range of functionalities for handling different protocols such as HTTP, HTTPS, FTP, LDAP, DICT, GOPHER, and FILE. Its features include custom time and speed limits, progress bar and time specs, authentication, resuming, proxy support, and file modification date retrieval. The library also supports SSL with OpenSSL engines and customizable telnet options for FTPS, among other advanced features. Additionally, TclCurl provides a standard proxy environment variable support, as well as a configuration file for ease of use. Overall, TclCurl is a useful library for handling network protocols in Tcl programs.