HypoMux

HypoMux aggregates multiple network connections on one Windows machine so a download can pull from Ethernet, Wi-Fi, and a phone hotspot at the same time. It assigns each new connection to an adapter rather than splitting a single TCP stream, so it speeds up anything that opens many connections at once: Steam, IDM, game launchers, big browser downloads. AGPL-3.0, free, no paid tier.

Installation is a signed Windows installer, with Authenticode signing through SignPath, more supply chain hygiene than most single-maintainer Windows projects bother with. System Proxy mode takes over the Windows proxy setting and works with anything proxy-aware. Virtual NIC mode uses Wintun and sing-box to catch broader traffic, and because it owns routing, DNS, and WFP it cannot share the default route with another TUN, so it will fight your VPN client. The UI runs unelevated and hands privileged work to a separate service, which is the correct design.

Solo on a mediocre connection with a second link available: this is the tool, and the price is zero. Anyone already saturating one pipe gets nothing, because HypoMux cannot make a single connection faster than that connection allows. Speedify is the commercial equivalent at $14.99 a month and bonds traffic through its own servers; HypoMux does the local half free and keeps your packets on your own links.

Windows 10 and 11 only, and the README is upfront that this is for your own devices and connections, not for getting around anyone's access controls. One maintainer, who is also the sole approver on the signing key. The engineering is careful, but the bus factor is one.