Playable demos:

Descent 3 (28.0MB, 28 Nov 98) - Contains one single-player and one multiplayer level.

Descent 1 (2.8MB, 27 Dec 94) - Contains first seven levels of retail version.

Descent 2 (3.9MB, 15 Dec 95) - Contains first three levels of retail version.

Descent: Freespace (v1.0, 26.8MB, 29 Apr 98) - Contains three single-player missions.  Note: also get the update patch below.

Descent Mission Builder 2 (1.0MB, 24 Feb 98) - A demo of the popular level design program for Descent 1 and 2.  It is limited to building 100-cube levels.

Non-playable demos/Trailers:

Descent 3 (unofficial recording of the demo at E3, 3 Jul 98, 6.9MB)

Descent 2 (16.1MB)

Descent 1 (3.1MB)

Descent: Freespace (v2.0, 28 Mar 98, 13.1MB)

Update patches:

Descent 1: Descent 1 1.0 -> 1.4a patch (559kB) Descent 1 1.4a -> 1.5 patch (239kB) Descent 1 eXtended 1.20 (20 Sep 98, unofficial, 350kB)

Descent 2: Descent 2 1.0/1.1 -> 1.2 patch (801kB) Descent 2 Win95/DirectX patch (1.9MB) - DirectX is required. (1.5MB)

Descent: Freespace: D:FS 1.0x -> 1.05 patch US version (5.1MB)    UK version (3.7MB)    French version (3.4MB)    German version (3.4MB)    Rest of the World version (2.9MB)

Descent: Freespace playable demo: D:FS demo 1.0/1.1 -> 1.2 patch (1.0MB)

3D Accelerator patches:

Descent 1: 3Dfx Voodoo (D1_3Dfx) unofficial patch (29 Aug 98, 1.7MB, beta 01) Direct 3D (D1_D3D) unofficial alpha patch (11 Sep 98, 211kB, early alpha)

Descent 2: 3Dfx Voodoo (D2VOODOO) official patch (760kB) 3Dfx Voodoo/Voodoo 2 (D2_3Dfx) unofficial 3Dfx beta patch (4 Mar 98, 790kB, v1.06) Verite (Rendition 1000) patch (706kB) S3 Virge (Stealth 3D) patch (1.2MB)